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Tachymeter Bezel
Rolex Oyster Perpetual Cosmograph Daytona,
Tachymeter Bezel

On the bezel or all the way around the dial, a tachymeter scale is frequently carved. You can determine speed, based on the amount of time spent going a specific distance when it starts at 500 units, which is often around the 7-second mark. A fixed tachymeter bezel is used in conjunction with a chronograph. It is used to convert speed for up to 60-second occurrences to seconds of elapsed time.

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