How to use the tachymeter on your chronograph watch
The tachymeter is a measuring instrument that tells you how quickly an object is moving. The tachymeter feature is found on some chronograph watch models.
WHAT IS A CHRONOGRAPH WATCH?
A chronograph watch comprises two separate systems:
A classic system that gives the time
and a chronograph system that shows how long an event lasts. It is usually found in the middle of the dial.
The chronograph system may function as a tachymeter that lets you calculate average speed usually over a distance of 1,000 m.
Find a reference point and press the pusher to activate the tachymeter (usually the top pusher). Press the same pusher again 1,000 m further on. Look where the second hand stopped on the tachymetric scale, that is your average speed. Remember: If the second hand goes over 60 seconds, then you’ll need to look at the average speed on the tachymeter’s second bezel. However, some watches don’t have a second bezel, in which case you will have to calculate the speed over 500 m and then multiply it by two. That being said, tachymeters are more accurate over longer distances. For more information, you can watch the video made by Baume & Mercier on the topic: