Complication
Tachymeter
A bezel scale that converts elapsed time into speed.
What it does
A fixed scale — usually on the bezel — that reads speed over a known distance. Paired with the chronograph seconds hand, it turns elapsed time into units per hour. It's the ring of numbers (400, 200, 100…) around many racing chronographs.
How to read it
Start the chronograph as an object covers a measured mile (or km); stop it at the finish. The chronograph hand points to the speed on the tachymeter scale. Only works for events under 60 seconds.
Impact on value
Neutral; part of the sporty-chronograph look (e.g. Daytona, Speedmaster).
Keep reading
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Knows the date, month, and leap years — until 2100.
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Tourbillon
A rotating cage that averages out gravity's error.
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World Time
All 24 time zones readable at once.
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Annual Calendar
Knows every month length except February.
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Alarm
A mechanical buzzer on your wrist.