How do you read a tachymeter? The video guide

Chapters

1. 0:00A calculator, not decoration
2. 0:17Tachymeter and chronograph
3. 0:29Start, stop, read
4. 0:4440 seconds, 90 km/h
5. 0:563,600 divided by the time
6. 1:17Speed, and also rate
7. 1:32The 60-second limit
8. 1:50Between 10 and 60 seconds

Transcript

That ring of numbers around the dial, running from sixty up to several hundred: many people take it for decoration. It is a calculator. It gives you a speed, without any arithmetic. It is the tachymeter. It works with the chronograph, the function that measures a length of time, over a known distance: one kilometre, for instance. At the start of the kilometre, you start the chronograph. At the finish, you stop it. The number the long hand points to on the ring is the average speed, in kilometres per hour. An example, as a passenger. One kilometre in forty seconds. The hand stops at ninety: the car was doing ninety kilometres per hour. The secret is a single division. Three thousand six hundred, the number of seconds in an hour, divided by the time measured. Three thousand six hundred divided by forty: ninety. The numbers on the ring have done the sum in advance. The ring has no unit. Over a mile, it gives miles per hour. And it also measures a rate: a task done in twenty seconds means one hundred and eighty tasks per hour. Its limit: beyond sixty seconds, the hand has gone all the way round the dial, and the ring is no longer any use. For a slower speed, measure over five hundred metres, then divide the number by two. And the faster it is, the less precise it gets. Eight seconds gives four hundred and fifty; nine seconds, four hundred. A single second apart, fifty kilometres per hour of difference. At thirty seconds, that same second changes only four kilometres per hour. For a reliable reading, choose a distance that takes between ten and sixty seconds. Discover a whole selection of watches at Montres Outlet.