A friend of mine, upon noticing my watch has a tachymeter on it, asked what it was & what it's purpose is. So, I Googled it today & found, firstly the correct spelling,( which the spell check does NOT agree with! Should be tachyometer! OH well...) then what it is & how it is used. I can't get the thing to turn, let alone operate it the way this article indicates!
On some of the analog watches or wristwatches from branch such as Omega and Casio, there is a outer scale bezel that inscribed around the rim and named tachymeter (also known as tachymetre or tacheometer). If you flip through the watch’s user guide or manual, you will not likely to find any explanation or definition on what is tachymeter or how to use the tachymeter functionality. Tachymeter is actually a tool used to compute speed based on travel time over a fixed distance travelled (like one mile or one kilometer). Thus, the tachymeter bezel or dial is a logarithmic scale (actually it’s not, as spacings between the marks on the tachymeter dial are proportional to 1/t where t is the elapsed time) that simplifies the computation of speed of an object, by computing the following function:
Tachymeter Dial = 3600 / Elapsed Time In Seconds