WO2009036809A1

WO2009036809A1 - Timepiece with density altitude indicator

Info

Publication number: WO2009036809A1
Application number: PCT/EP2007/060026
Authority: WO
Inventors: Yeslam Binladin
Original assignee: SENSES Ltd
Current assignee: SENSES Ltd
Priority date: 2007-09-21
Filing date: 2007-09-21
Publication date: 2009-03-26
Anticipated expiration: 2010-03-21

Abstract

The invention concerns a timepiece (1) with an integrated density altitude indicator, which comprises a case that is closed by a glass (5) and formed of a back cover (2) and a middle part (3); a time display (6); a bezel (7) comprising a ro- tatable part (8) with a circular first edge (9); a time keeping circuit (10) controlling the time display (6); and at least one energy source (11) powering the time-keeping circuit (10). One preferred embodiment of the timepiece according to the invention is characterized in that the bezel (7) comprises field elevation (ELEVATION) marks and Outside Air Temperature (O.A.T.) marks that are in each case directed radial to the first edge (9) of the rotatable part (8) of the bezel (7) and that are diametrically opposed to each other. The inventive timepiece (1) comprises an indicator ring (12) with a circular first edge (13) that is concentrically arranged with and that is located close to the first edge (9) of the rotatable part (8) of the bezel (7). The fixed indicator ring (12) comprises Outside Air Temperature (O.A.T.) marks and density altitude (DENSITY AIt.) marks that are in each case directed radial to the first edge (13) of the indicator ring (12) and that are diametrically opposed to each other in such a way that the (ELEVATION) marks of the rotatable part (8) of the bezel (7) are located opposite the (O.A.T.) marks of the indicator ring (12) and that the (O.A.T.) marks of the rotatable part (8) of the bezel (7) are located opposite the (DENSITY Alt.) marks of the indicator ring (12). Also disclosed are uses of the inventive timepiece for estimating the density altitude of an air field.

Description

Timepiece with density altitude indicator

The present invention relates to a timepiece with density altitude indicator. The timepiece comprises: a case formed of a back cover and a middle part, the case being closed by a glass; a time display; a bezel mounted on the middle part and surrounding the time display, the bezel comprising a rotatable part with a circular first edge; a time keeping circuit disposed in the case and controlling the time display; and at least one energy source powering the timekeeping circuit. The invention more particularly concerns a wristwatch or pocket watch enabling a user, particularly a pilot, to estimate the density altitude when being on a flight deck or not.

There are many factors in aviation that a pilot has to take into consideration. One particular item of special interest the present invention is concerned with is the "density altitude". As educated pilots know, the input for a standard altimeter is static air pressure. An altimeter is an active instrument used to measure the altitude of an object above a fixed level. The altimeter is calibrated to show the pressure directly as an altitude, in accordance with a mathematical model defined by the International Standard Atmosphere (ISA). In aviation terminology, the regional or local air pressure at mean sea level (MSL) is called the QNH or "altime- ter setting". With this setting, the altimeter will read the airport elevation. The pressure, which will calibrate the altimeter to show the height above ground at a given airfield, is called the QFE of the field. An altimeter cannot, however, be ad- justed for variations in air temperature. Differences in temperature from the ISA model will, therefore, cause errors in indicated altitude.

The ,,density altitude" is the altitude at which the density of the International Standard Atmosphere (ISA) is the same as the density of the air being evaluated. The Standard Atmosphere ISA is simply a mathematical model of the atmosphere, which is standardized so that predictable calculations can be made. So, the basic idea of calculating ,,density altitude" is to calculate the actual density of the air, and then finding the altitude at which the same air density occurs in the standard atmosphere. Air density is affected by air pressure, air temperature and humidity. The density of the air is reduced by decreased air pressure, increased temperatures and increased moisture. A reduction in air density reduces the engine horsepower, reduces aerodynamic lift and reduces drag.

When an aircraft climbs, a decrease in both the air temperature (-2 ⁰C per 1000 feet or about 300 meters) as well as the air pressure (37 mbar per 1000 feet or about 300 meters) is experienced. For reference purposes, the length of a foot is approximated by 0.3 m. In the following, it is referred to the conditions of the International Standard Atmosphere (ISA) as it is widely known and accepted. The ISA is an atmospheric model of how the pressure, temperature, density, and viscosity of the earth's atmosphere change over a wide range of altitudes. The ISA consists of tables of values at various altitudes, plus some formulas by which those values were derived. The International Organization for Standardization (ISO) publishes the ISA as an international standard ISO 2533 : 1975. Other stan- dards organizations, such as the International Civil Aviation Organization (ICAO) and the United States Government, publish extensions or subsets of the same atmospheric model under their own standards-making authority. The (ICAO) published their "ICAO Standard Atmosphere" as Doc 7488-CD in 1993. It has the same model as the ISA, but extends the altitude coverage to 80 kilometers (262,500 feet). The ISA model divides the atmosphere into layers with linear temperature distributions. The other values are computed from basic physical constants and relationships. Thus the standard consists of a table of values at various altitudes. For example, at sea level the standard gives a pressure of 1.013 bar and a temperature of 15°C, and an initial lapse rate of -6.5 °C/km. Above 12 km, the tabulated temperature is essentially constant. The tabulation continues to 18 km where the pressure has fallen to 0.075 bar and the temperature to -56.5 ⁰C. The ISA model is based on average conditions at mid latitudes, as determined by ISO's TC 20/SC 6 technical committee. It has been revised from time to time since the middle of the 20th century.

Although the concept of "Density Altitude" is commonly used to help express the effects of aircraft performance, the really underlying property of interest is actually the air density. For example, the lift of an aircraft wing, the aerodynamic drag and the thrust of a propeller blade are all directly proportional to the air density. Similarly, the horsepower output of an internal combustion engine is related to the air density. Density altitude has been a convenient yardstick for pi- lots to compare the performance of an aircraft at various altitudes, but it is in fact the air density that is the fundamentally important quantity, and "Density Altitude" is simply one way to express the air density. Both, increase in temperature and increase in humidity cause a reduction in air density. Thus, in hot and humid conditions the density altitude at a particular location may be significantly higher than the geometric altitude.

The importance of "Density Altitude" is best understood during the flight planning stage of a flight. Whereas elevation is very important, for matters such as ap- proaches and terrain clearance, it is "Density Altitude" a pilot needs to know, because this is the altitude he can use for runway and engine performance calculations. With an increase in density altitude, the airplane is negatively affected in certain aspects. For example, with an decrease in air density the take off roll increases and also, engine performance decreases. Needless to say that this has a big influence on a go/no go decision. As said, density altitude increases with increasing temperature and humidity. Thus in hot and humid conditions, the density altitude may be significantly higher than the geometric altitude or airport elevation. For an accurate calculation of the density of the air, i.e., the "Density Altitude", a lot of variables are required, which are than used in extensive calcu- lations. From the prior art, there are methods known for calculation of the Density Altitude with e.g. a Density Altitude Computation Chart.

It is the objective of the present invention to provide a timepiece with density altitude indicator.

This objective is achieved according to a first aspect, by a timepiece as previously described and according to the features of the independent claim 1. The timepiece according to the invention is characterized in that the bezel comprises (ELEVATION) marks and Outside Air Temperature (O. A. T.) marks that are in each case directed radial to the first edge of the rotatable part of the bezel and that are diametrically opposed to each other, wherein the timepiece comprises an indicator ring with a circular first edge that is concentrically arranged and that is located close to the first edge of the rotatable part of the bezel, the indicator ring being fixed to the middle part of the timepiece and comprising Outside Air Temperature (O. A. T.) marks and density altitude (DENSITY Alt.) marks that are in each case directed radial to the first edge of the indicator ring and that are diametrically opposed to each other in such a way that the (ELEVATION) marks of the rotatable part of the bezel are located opposite the (O. A. T.) marks of the indicator ring and that the (O. A. T.) marks of the rotatable part of the bezel are located opposite the (DENSITY Alt.) marks of the indicator ring.

This objective is achieved according to a second aspect, by a timepiece as previ- ously described and according to the features of the independent claim 4. The timepiece according to the invention is characterized in that the bezel comprises Outside Air Temperature (O. AT.) marks and density altitude (DENSITY Alt.) marks that are in each case directed radial to the first edge of the rotatable part of the bezel and that are diametrically opposed to each other, wherein the time- piece comprises an indicator ring with a circular first edge that is concentrically arranged and that is located close to the first edge of the rotatable part of the bezel, the indicator ring being fixed to the middle part of the timepiece and comprising (ELEVATION) marks and Outside Air Temperature (O. A. T.) marks that are in each case directed radial to the first edge of the indicator ring and that are diametrically opposed to each other in such a way that the (O. A. T.) marks of the rotatable part of the bezel are located opposite the (ELEVATION) marks of the indicator ring and that the (DENSITY Alt.) marks of the rotatable part of the bezel are located opposite the (O. A. T.) marks of the indicator ring.

Additional preferred and inventive elements and features derive from the dependent claims in each case. Also disclosed are uses of the inventive timepiece for estimating the density altitude on the flight deck of an aircraft that is equipped with an altimeter or for estimating the density altitude of an airfield.

The timepiece of the invention is now described in greater detail on the basis of exemplary embodiments and with the help of accompanying schematic drawings that illustrate a preferred embodiment of the present invention and that are not intended to limit the scope of the invention. It is shown in : Fig. 1 a plain view of a timepiece with an analogue time display and an integrated density altitude indicator according to a first embodiment of the arrangement of the bezel and the indicator ring;

Fig. 2 a cross section through a timepiece with a first and second variant to the first embodiment of the arrangement of the bezel and the indicator ring as shown in Fig. 1.

Figure 1 shows a plain view of a timepiece 1 with an analogue time display and an integrated density altitude indicator according to a first embodiment of the arrangement of the bezel 7 and the indicator ring 12. The timepiece 1 comprises a case formed of a back cover 2 and a middle part 3, the case being closed by a glass 5 (see Fig. 2). The timepiece further comprises a time display 6; a bezel 7 mounted on the middle part 3 and surrounding the time display 6. The bezel 7 comprises a rotatable part 8 with a circular first edge 9. The timepiece also comprises a time keeping circuit 10 disposed in the case and controlling the time display 6 and at least one energy source 11 powering the timekeeping circuit 10 (see Fig. 2).

The bezel 7 of the timepiece 1 of the present invention - according to the first embodiment - comprises (ELEVATION) marks and Outside Air Temperature (O.A.T.) marks that are in each case directed radial to the first edge 9 of the rotatable part 8 of the bezel 7 and that are diametrically opposed to each other. The inventive timepiece 1 comprises an indicator ring 12 with a circular first edge 13 that is concentrically arranged with and that is located close to the first edge 9 of the rotatable part 8 of the bezel 7. The indicator ring 12 is fixed to the middle part 3 of the timepiece 1 and comprises Outside Air Temperature (O.A.T.) marks and density altitude (DENSITY Alt.) marks that are in each case directed radial to the first edge 13 of the indicator ring 12 and that are diametrically opposed to each other in such a way that the (ELEVATION) marks of the rotatable part 8 of the bezel 7 are located opposite the (O.A.T.) marks of the indicator ring 12 and that the (O.A.T.) marks of the rotatable part 8 of the bezel 7 are located opposite the (DENSITY Alt.) marks of the indicator ring 12. The timepiece 1 preferably comprises an analogue time display 6 with 12 hour positions and with an hour hand 14 and a minute hand 15, and a crown 4 at the three o'clock position. On this exemplary timepiece 1, the (ELEVATION) marks of the rotatable part 8 of the bezel 7 and the opposed (O. A. T.) marks of the indica- tor ring 12 are located on a top side 18 of the timepiece 1, preferably between the 10 o'clock and 2 o'clock positions. The (O. A. T.) marks of the rotatable part 8 of the bezel 7 and the opposed (DENSITY AIt.) marks of the indicator ring 12 of this exemplary timepiece 1 are located on a bottom side 19 of the timepiece 1, preferably between the 4 o'clock and 8 o'clock positions.

Alternatively (not shown), the timepiece 1 comprises a digital time display 6. The (ELEVATION) marks of the rotatable part 8 of the bezel 7 and the opposed (O. A. T.) marks of the indicator ring 12 of this alternative variant preferably are located on a top side 18 of the timepiece 1, wherein the (O. A. T.) marks of the ro- tatable part 8 of the bezel 7 and the opposed (DENSITY Alt.) marks of the indicator ring 12 preferably are located on a bottom side 19 of the timepiece 1 with a digital time display.

According to a second embodiment of the arrangement of the bezel 7 and the in- dicator ring 12 (not shown), the timepiece 1 comprises the same basic elements, a case that is closed by a glass 5 and formed of a back cover 2 and a middle part 3; a time display 6; a bezel 7 comprising a rotatable part 8 with a circular first edge 9; a time keeping circuit 10 disposed in the case and controlling the time display 6; and at least one energy source 11 powering the timekeeping circuit 10 (see Fig. 2).

The bezel 7 of the timepiece 1 of the present invention - according to the second embodiment - comprises Outside Air Temperature (O. A. T.) marks and density altitude (DENSITY Alt.) marks that are in each case directed radial to the first edge 9 of the rotatable part 8 of the bezel 7 and that are diametrically opposed to each other. The inventive timepiece 1 comprises an indicator ring 12 with a circular first edge 13 that is concentrically arranged with and that is located close to the first edge 9 of the rotatable part 8 of the bezel 7. The indicator ring 12 is fixed to the middle part 3 of the timepiece 1 and comprises (ELEVATION) marks and Outside Air Temperature (O. A. T.) marks that are in each case directed radial to the first edge 13 of the indicator ring 12 and that are diametrically opposed to each other in such a way that the (O. AT.) marks of the rotatable part 8 of the bezel 7 are located opposite the (ELEVATION) marks of the indicator ring 12 and that the (DENSITY Alt.) marks of the rotatable part 8 of the bezel 7 are located opposite the (O. A. T.) marks of the indicator ring 12.

The timepiece 1 preferably comprises an analogue time display 6 with 12 hour positions and with an hour hand 14 and a minute hand 15, and a crown 4 at the three o'clock position. On this exemplary timepiece 1, the (O. A. T.) marks of the rotatable part 8 of the bezel 7 and the opposed (ELEVATION) marks of the indicator ring 12 are located on a top side 18 of the timepiece 1, preferably between the 10 o'clock and 2 o'clock positions wherein the (DENSITY AIt.) marks of the rotatable part 8 of the bezel 7 and the opposed (O. A. T.) marks of the indicator ring 12 are located on a bottom side 19 of the timepiece 1, preferably between the 4 o'clock and 8 o'clock positions.

Alternatively (not shown), the timepiece 1 comprises a digital time display 6 and the (O. A. T.) marks of the rotatable part 8 of the bezel 7 and the opposed

(ELEVATION) marks of the indicator ring 12 are located on a top side 18 of the timepiece 1, wherein the (DENSITY Alt.) marks of the rotatable part 8 of the bezel 7 and the opposed (O. A. T.) marks of the indicator ring 12 are located on a bottom side 19 of the timepiece 1.

Figure 2 shows a cross section through a timepiece 1 with a first and second variant to the first embodiment of the arrangement of the bezel 7 and the indicator ring 12 as shown in Fig. 1. All basic and all inventive elements of a timepiece 1 are shown here: The case is closed by a glass 5 and formed of a back cover 2 and a middle part 3. There is a time display 6 and a bezel 7 comprising a rotatable part 8 with a circular first edge 9. A time keeping circuit 10 is disposed in the case and controlling the time display 6. Also disposed in the case is at least one energy source 11 that powers the timekeeping circuit 10. _ g _

In this Figure 2, there are two alternative variants of the arrangement of the bezel 7 and the indicator ring 12 disclosed. On the left, the indicator ring 12 visually is a part of the bezel 7 of the timepiece 1 and located above the glass 5. However, also in this case, the indicator ring 12 is fixed and cannot be rotated. Thus, only the rotatable part 8 of the bezel 7 can be rotated with respect to the indicator ring 12. This variant according to the left side in Figure 2 has the advantage that the two circular edges 9,13 of the rotatable bezel part 8 and of the indicator ring 12 are in very close proximity. This enables precise alignment of the scales of the rotatable bezel part 8 and of the indicator ring 12 and readout of the density altitude (DENSITY Alt.) value without optical parallax error.

On the right, the indicator ring 12 is a part of the middle part 3 and located below the glass 5. As it is obvious in this case, the indicator ring 12 is fixed and cannot be rotated and only the rotatable part 8 of the bezel 7 can be rotated with re- spect to the indicator ring 12. This variant according to the right side in Figure 2 has the advantage that the area of the rotatable bezel part 8 and of the indicator ring 12 in each case can be larger. This allows larger and better readable scales and letters to be applied to the rotatable bezel part 8 and to the indicator ring 12 and, thus, easier readout of the density altitude (DENSITY AIt.) value.

It is preferred that the rotatable part 8 of the bezel 7 of the timepiece 1 according to the invention comprises a surface that presents a surface with enhanced grip. This surface can be corrugated or corded, however a rubber application 16 attached to at least a part of the circumference 17 of the rotatable part 8 of the bezel 7 is preferred. Also combinations of corded surface and pieces of rubber applications are conceivable. Especially preferred is a ring-like rubber application 16 around the circumference 17 of the rotatable bezel part 8 as shown in Fig. 1.

The time keeping circuit 10 or movement of the timepiece 1 can be mechanical or electronic. Mechanical movements are well known as "tourbillon" or as "automatic" clockworks. A tourbillon is a type of mechanical clock or watch escapement invented in 1795 by Abraham-Louis Breguet that is designed to counter the effects of gravity and other perturbing forces that can affect the accuracy of a chronometer. In a tourbillon, the entire escapement assembly rotates, including balance wheel, escapement wheel, and pallet fork. The rate of rotation varies per design but has generally become standardized at one rotation per minute. Thus, the energy source 11 in tourbillon is the entire escapement assembly. There are many "Tourbillon" fake/replicas of premium brand watches that emulate this feature with the oscillating balance wheel visible through the watch dial. However, these are usually conventional lever escapements of automatic clockworks, not tourbillons.

Electronic movements are well known as "quartz" clockworks. A quartz clock is a clock that uses an electronic oscillator that is made of a quartz crystal to keep precise time. This crystal oscillator creates a signal with very precise frequency. Generally, a time keeping circuit 10 in some form of digital logic counts the cycles of this signal and provides a numeric time display. The energy source 11 in a quartz timepiece usually is an electrical source implemented as a battery or an accumulator.

Irrespective of the type of the time keeping circuit 10 or movement and of the energy source 11 of the timepiece 1, the bezel 7 with its (ELEVATION) marks and Outside Air Temperature (O.A.T.) marks and the indicator ring 12 with its Outside Air Temperature (O.A.T.) marks and density altitude (DENSITY Alt.) marks (according to the first embodiment of the invention) are usable for the estimation of the density altitude in a simple aircraft without a density altitude computation chart. The same is true for the or second embodiment of the invention, in which the scales with the (ELEVATION) marks and Outside Air Temperature (O.A.T.) marks as well as with the Outside Air Temperature (O.A.T.) marks and density altitude (DENSITY Alt.) marks are interchanged on the bezel 7 and on the indicator ring 12. However, one especially preferred embodiment of the timepiece 1 according to the invention is based on an automatic movement (time keeping cir- cuit 10) and incorporates an analogue time display 6 with an hour hand 14 and minute hand 15. The timepiece 1 preferably is embodied as a wristwatch or as a pocket watch. Especially preferred is the embodiment of the inventive timepiece 1 as a wrist- watch.

The use of the timepiece 1 according to the invention for estimating the density altitude is now explained on the base of the first embodiment of the invention as shown in the figures 1 and 2:

When not on the flight deck: First, the actual field elevation (ELEVATION) is obtained from legal documents, such as an approach plate or a current map. Than, the outside air temperature (O. A. T.) is taken from an outside air thermometer or from the most recent meteorological report and the (ELEVATION) value and the (O. A. T.) value are aligned on a top side 18 of the timepiece 1. Preferably, the outside air temperature (O. A. T.) value in ⁰C is on the inner scale, i.e., on the indicator ring 12, and the actual field elevation (ELEVATION) in feet is on the outer scale, i.e., on the ro- tatable part 8 of the bezel 7. As an example, an actual field elevation (ELEVATION) value of 7000 feet and an outside air temperature (O. AT.) of 30 ⁰C are indicated with a bold arrow in Fig. 1.

Than, the corresponding outside air temperature (O. A. T.) is found in ⁰C on a bottom side 19 of the timepiece 1. Preferably, the outside air temperature (O. A. T.) value is on the outer scale, i.e., on the rotatable part 8 of the bezel 7 (see solid arrow in Fig. 1). Now, opposite the outside air temperature (O. A. T.) on the bot- torn side 19 of the timepiece 1, preferably on the inner scale (the indicator ring 12), the density altitude (DENSITY Alt.) value is estimated. According to this example, the density altitude of the airfield is estimated to be about 10'0OO feet.

When on the flight deck of an aircraft that is equipped with an altimeter: First, the field elevation (ELEVATION) is obtained by setting the altimeter to the local or reported QNH. Then, the outside air temperature (O. A. T.) is taken from reading the value from an outside thermometer or by using the outside air temperature from the most recent meteorological report. Now, the actual (O. A. T.) and (ELEVATION) values are preferably aligned on a top side 18 of the timepiece 1. Preferably, the current (O. A. T.) value in ⁰C is on the inner scale, i.e., on the indicator ring 12, and the current field elevation (ELEVATION) in feet is on the outer scale, i.e., on the rotatable part 8 of the bezel 7.

Than, the corresponding outside air temperature (O. A. T.) in ⁰C is found on a bottom side 19 of the timepiece 1, preferably on the outer scale, i.e., on the rotatable part 8 of the bezel 7. Now, opposite the outside air temperature (O. A. T.) on the bottom side 19 of the timepiece 1, the actual density altitude (Density Alt.) value is estimated.

Whereas the scales on the timepiece of the invention are based on the ISA conditions, they can practically arbitrary chosen in a wide range as follows: The Outside Air Temperature (O. A. T.) is indicated between -30 ⁰C and +50 ⁰C. The Elevation is indicated between 500 and 10'0OO feet above mean sea level. The Density Altitude is indicated between -2'00O and +15'0OO feet above mean sea level.

The particularly preferred scales on the timepiece of the invention are based on the ISA conditions as follows:

The Outside Air Temperature (O. AT.) is indicated between -15 ⁰C and +35 ⁰C. The Elevation is indicated between 1'0OO and 7'00O feet above mean sea level. The Density Altitude is indicated between -2'00O and +10O00 feet above mean sea level.

Any combinations of the features of the individual embodiments disclosed herein belong to the scope of the present invention. The same reference numbers are given to the same features shown in the drawings, even when they are not specifically addressed in the specification in each case. List of reference numerals:

1 timepiece, wrist watch, pocket watch

2 back cover

3 middle part

4 crown

5 glass

6 time display

7 bezel

8 rotatable part of 7

9 circular first edge of 8

10 time keeping circuit

11 energy source

12 indicator ring

13 first edge of 12

14 hour hand

15 minute hand

16 rubber application

17 circumference of 8

18 top side of 1

19 bottom side of 1

Claims

Patent Claims

1. A timepiece ( 1) comprising : a case formed of a back cover (2) and a middle part (3), the case being closed by a glass (5);

- a time display (6); a bezel (7) mounted on the middle part (3) and surrounding the time display (6), the bezel (7) comprising a rotatable part (8) with a circular first edge (9); - a time keeping circuit (10) disposed in the case and controlling the time display (6); and at least one energy source (11) powering the timekeeping circuit (10); characterized in that the bezel (7) comprises field elevation (ELEVATION) marks and Outside Air Temperature (O. A. T.) marks that are in each case di- rected radial to the first edge (9) of the rotatable part (8) of the bezel (7) and that are diametrically opposed to each other, wherein the timepiece (1) comprises an indicator ring (12) with a circular first edge (13) that is concentrically arranged with and that is located close to the first edge (9) of the rotatable part (8) of the bezel (7), the indicator ring (12) being fixed to the middle part (3) of the timepiece (1) and comprising Outside Air Temperature (O.A.T.) marks and density altitude (DENSITY Alt.) marks that are in each case directed radial to the first edge (13) of the indicator ring (12) and that are diametrically opposed to each other in such a way that the (ELEVATION) marks of the rotatable part (8) of the bezel (7) are located opposite the (O.A.T.) marks of the indicator ring (12) and that the (O.A.T.) marks of the rotatable part (8) of the bezel (7) are located opposite the (DENSITY Alt.) marks of the indicator ring (12).

2. The timepiece of claim 1, comprising a analogue time display (6) with 12 hour positions and with an hour hand (14) and a minute hand (15), and a crown (4) at the three o'clock position, characterized in that the

(ELEVATION) marks of the rotatable part (8) of the bezel (7) and the opposed (O.A.T.) marks of the indicator ring (12) are located on a top side (18) of the timepiece ( 1), preferably between the 10 o'clock and 2 o'clock positions, wherein the (O. A. T.) marks of the rotatable part (8) of the bezel (7) and the opposed (DENSITY Alt.) marks of the indicator ring (12) are located on a bottom side (19) of the timepiece (1), preferably between the 4 o'clock and 8 o'clock positions.

3. The timepiece of claim 1, comprising a digital time display (6), characterized in that the (ELEVATION) marks of the rotatable part (8) of the bezel (7) and the opposed (O. A. T.) marks of the indicator ring (12) are located on a top side (18) of the timepiece (1), wherein the (O. AT.) marks of the rotatable part (8) of the bezel (7) and the opposed (DENSITY AIt.) marks of the indicator ring (12) are located on a bottom side (19) of the timepiece.

4. A timepiece (1) comprising : - a case formed of a back cover (2) and a middle part (3), the case being closed by a glass (5); a time display (6); a bezel (7) mounted on the middle part (3) and surrounding the time display (6), the bezel (7) comprising a rotatable part (8) with a circular first edge (9); a time keeping circuit (10) disposed in the case and controlling the time display (6); and at least one energy source (11) powering the timekeeping circuit (10); characterized in that the bezel (7) comprises Outside Air Temperature (O. AT.) marks and density altitude (DENSITY Alt.) marks that are in each case directed radial to the first edge (9) of the rotatable part (8) of the bezel (7) and that are diametrically opposed to each other, wherein the timepiece ( 1) comprises an indicator ring (12) with a circular first edge ( 13) that is concentrically arranged with and that is located close to the first edge (9) of the rotatable part (8) of the bezel (7), the indicator ring (12) being fixed to the middle part (3) of the timepiece (1) and comprising field elevation (ELEVATION) marks and Outside Air Temperature (O. AT.) marks that are in each case directed radial to the first edge (13) of the indicator ring (12) and that are diametrically opposed to each other in such a way that the (O, A. T.) marks of the rotatable part (8) of the bezel (7) are located opposite the (ELEVATION) marks of the indicator ring (12) and that the (DENSITY Alt.) marks of the rotatable part (8) of the bezel (7) are located opposite the (O. A. T.) marks of the indicator ring (12).

5. The timepiece of claim 4, comprising a analogue time display (6) with 12 hour positions and with an hour hand (14) and a minute hand (15), and a crown (4) at the three o'clock position, characterized in that the (O. A. T.) marks of the rotatable part (8) of the bezel (7) and the opposed (ELEVA¬

TION) marks of the indicator ring (12) are located on a top side (18) of the timepiece (1), preferably between the 10 o'clock and 2 o'clock positions, wherein the (DENSITY AIt.) marks of the rotatable part (8) of the bezel (7) and the opposed (O.A.T.) marks of the indicator ring ( 12) are located on a bottom side (19) of the timepiece ( 1), preferably between the 4 o'clock and

8 o'clock positions.

6. The timepiece of claim 4, comprising a digital time display (6), characterized in that the (O.A.T.) marks of the rotatable part (8) of the bezel (7) and the opposed (ELEVATION) marks of the indicator ring (12) are located on a top side (18) of the timepiece (1), wherein the (DENSITY AIt.) marks of the rotatable part (8) of the bezel (7) and the opposed (O.A.T.) marks of the indicator ring (12) are located on a bottom side (19) of the timepiece.

7. The timepiece (1) of one of the preceding claims, characterized in that the indicator ring (12) is a part of the bezel (7) and located above the glass.

8. The timepiece (1) of one of the claims 1 to 6, characterized in that the indicator ring (12) is a part of the middle part (3) and located below the glass.

9. The timepiece ( 1) of one of the preceding claims, characterized in that the rotatable part (8) of the bezel (7) comprises a rubber application (16) attached to at least a part of its circumference ( 17).

10. The timepiece (1) of one of the preceding claims, characterized in that it is embodied as a wristwatch or as a pocket watch.

11. Use of the timepiece (1) of one of the claims 1 or 4 for estimating the den- sity altitude on the flight deck of an aircraft that is equipped with an altimeter, characterized in that the use comprises the steps of: obtaining the field elevation (ELEVATION) by setting the altimeter to the local or reported QNH; taking the outside air temperature (O. A. T.); - aligning the actual (ELEVATION) and (O. A. T.) values on a top side (18) of the timepiece ( 1); finding the corresponding outside air temperature (O. A. T.) on a bottom side (19) of the timepiece (1); and estimating opposite the outside air temperature (O. A. T.) on the bottom side ( 19) of the timepiece (1) the (Density Alt.) value.

12. Use of the timepiece (1) of one of the claims 1 or 4 for estimating the density altitude of an air field, characterized in that the use comprises the steps of: - obtaining the actual field (ELEVATION) from legal documents; taking the outside air temperature (O. A. T.); aligning the (ELEVATION) value and the (O. A. T.) value on a top side

(18) of the timepiece (1); finding the corresponding outside air temperature (O. A. T.) on a bottom side (19) of the timepiece (1); and estimating opposite the corresponding outside air temperature (O. A. T.) on the bottom side (19) of the timepiece (1) the (Density Alt.) value.

13. The use of one of the claims 11 or 12, characterized in that the timepiece ( 1) is embodied as a wristwatch or as a pocket watch.