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Tachymeter watches


Tachymeter scale - why and how?

The tachymeter scale is based on the formula: Speed = distance / time. The scale was developed to perform this calculation automatically when using the stopwatch function of the watch.

The speed displayed in the aircraft rarely corresponds to the speed flown over ground. With a tachymeter scale, a pilot can determine his speed based on a known distance. To do this, he stops the time he needs to cover a distance of 1 kilometre, for example.

If the pointer is at 100 on the tachymeter scale after covering the kilometre, for example, the pilot knows that he is currently flying at 100 km/h over ground.

Knowing your exact speed over ground can be important if, for example, you want to reach an airfield in a headwind and need to pay attention to the amount of fuel in the tank. If I still have fuel in the tank for an hour and know that I am travelling at 100 km/h, the destination airfield may only be a maximum of 50 km away. For safety reasons, you must always have half an hour's worth of fuel left in the tank when you land.

Tachymeter scale - why and how?

Time, distance, speed

The tachymeter scale is based on the formula: Speed = distance / time. The scale is designed to perform this calculation automatically when using the watch's stopwatch function.
Speed
Due to the wind, the speed displayed in an aeroplane rarely corresponds to the speed over ground. Using a tachymeter scale, a pilot can determine his speed based on a known distance. To do this, he stops the time he needs to cover a distance of 1 kilometre, for example. If the pointer is at 100 on the tachymeter scale after covering the kilometre, for example, the pilot knows that he is currently flying at 100 km/h over ground.
Time
Knowing your exact speed over ground can be important if, for example, you want to reach an airfield in a headwind and need to pay attention to the amount of fuel in your tank. If I have an hour's worth of fuel left in the tank and know that I am travelling at 100 km/h, the destination airfield may only be a maximum of 50 km away. For safety reasons, you must still have half an hour's worth of fuel left in the tank when you land.

Junkers JUMO Tachymeter