The Expedition series of watches offered by Timex include a tachymeter. This function is found on the analogue Expedition watches. A tachymeter is a round version of a slide rule. This is used for aviation and navigation purposes as it is a very precise "ratio-calculator" that allows air speed conversions, gas burning calculations and estimated time of arrival between destinations. With rare exception, watch makers do not include instructions on how to use the tachymeter. The physical use is very easy, but learning the calculation formulas takes a good deal of time and practice to get the learning curve down.
- Skill level:
- Moderately Challenging
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Place the Expedition on your wrist and look at the outer edge of the timepiece. Gently turn the outer edge, called the bezel, clockwise. Watch the red triangle on the edge turn with the bezel. The red triangle is the reference point used to set and calculate your data.
Read the very outside edge on the bezel. There are two sets of numbers along the bezel, the inner and outer. The outer numbers are always used to calculate speed and distance. The inner numbers are used for calculating things such as fuel consumption rates or wind corrections.
Press the upper right hand button on the Timex Expedition. Watch the left dial begin to turn (the small inset dial). This is a calibrated 60 increment dial. Use this to calibrate ETAs or distances with times. For example, pick a point on the ground as the aeroplane is moving through the air and press the upper right button as the plane passes over it.
Pick another point out on the ground at one mile ahead. As the plane passes over the second ground reference point, click the upper right hand button again to stop the dial from moving. If the time passed was more than the calibrated 60 seconds, the middle inset dial will move one increment clockwise. Use the two dials to reference the time it took to cover the randomly assigned distance.
Look at the numbers from the two dials. For example, if the dials indicate it took 15 seconds on the first dial, and you know you went 1 mile in that time, use the outer bezel to find the speed you are travelling, in this case 240 miles per hour.
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