Putting The Incredible Accuracy Of Mechanical Wristwatches Into Perspective
by John Keil
One thing that blows my mind each and every time I think of it is the remarkable accuracy of mechanical wristwatches.
Internally, I shake my head a bit when I hear someone complain that his or her watch is off by a few seconds per day.
I know some of you are thinking, “Well, I paid thousands of dollars, I expect it to be dead accurate.” And while I understand that train of thought, try digesting this information and see if I can convince you to be a little bit less critical.
The rate of a mechanical wristwatch is measured in Hz (hertz). One Hz is equal to two vibrations or one full oscillation per second. An oscillation is one turn of the balance wheel in one direction and then back in the other.
This being easy enough to understand, the majority of today’s mechanical wristwatches function at 4 Hz or 28,800 vph (vph = vibrations per hour, sometimes called bph for beats per hour).
Let’s put that into perspective: 28,800 vph x 24 hours = 691,200 complete oscillations per day.
The current standard tolerance for a C.O.S.C.-certified chronometer wristwatch is +6 / -4 seconds per day. A six-second interval contains 48 vibrations. The C.O.S.C. (Contrôle Officiel Suisse des Chronomètres) is the official institute in Switzerland for testing the precision of wristwatches.
This means that, in the worst case, if a chronometer-certified watch is off by six seconds in a day, that’s six out of 86,400 seconds in a day (24 hours x 60 minutes x 60 seconds).
Therefore, a C.O.S.C.-certified chronometer is 99.9930556 percent accurate at its worst!
And just imagine this, too: many of these incredible machines were designed and created more than a century or two ago without the aid of computers and modern technology.