How to use a Tachymeter in watches A tachymeter scale is a function which is usually inscribed around the rim of a dial or the bezel. It is used to compute speed on the basis of time travelled or can measure distance based on speed. A tachymeter is also used to calculate the number of tasks you can complete in a given time. The tachymeter scale on a watch generally starts at 500-700 and decreases as time elapses. The spacing between the marks on the tachymeter dial are therefore proportional to 1/t where t is the elapsed time, and hence the tachymeter scale is logarithmic and noticeably non linear. The simple equation to time versus speed and distance is used in calculation with a tachymeter. When you are using a tachymeter to calculate speed you can use the equation T=3600/t, where T stands for the tachymeter scale value, (t) is the elapsed time and 3600 is the number of seconds in an hour. When using a tachymeter to calculate distance, you first need to know the travelling speed (d). Start at the zero-seconds reading, and end once your tachymeter reading is your travelling speed. For example, say your speed is 75 mph. Once the tachymeter reading reaches 75, then you have travelled 1 mile. For this measurement to work, speeds must always remain at a constant 60 mph (or 60 of another unit of measurement) or faster. Some tachymeter scales are on a rotating, indexed bezel. This allows two additional modes of use: The tachymeter bezel can be aligned with a free running second hand, and, more subtly, can be used to find the average speed over longer times/distances. TO Read more about Luxury Swiss Watches with tachymeter, please visit the website http://www.ethoswatches.com/ .