Timing complication
What is a tachymeter?
A scale around the dial or bezel that converts the seconds it takes to cover a set distance into speed in units per hour.
How it works
A tachymeter turns elapsed time into speed. Start the chronograph as you pass one marker, stop it at the next marker one unit away, a mile or a kilometre, and read the number the seconds hand points to on the tachymeter scale. That number is your speed in units per hour.
The scale is simply 3,600 divided by the seconds: 3,600 seconds in an hour, so covering one unit in 36 seconds means 100 units an hour. Because of that, a standard scale only works between about 7.2 seconds (500 units per hour) and 60 seconds (60 units per hour).
It also works for rates of anything. Time how long it takes to make one item and the scale shows how many you'd make in an hour.
History
Tachymeter scales appeared on chronographs in the early 20th century for motor racing, where timekeepers and drivers needed quick speed readings. The Omega Speedmaster put the scale on its bezel in 1957, and the Rolex Daytona, Heuer Carrera and countless racing chronographs followed.
Before you buy
Almost nobody uses the tachymeter for speed today, but it's part of the classic racing chronograph look. If you like a cleaner dial, look for chronographs without one; if you want the Speedmaster look, it's essential.
Tachymeter watches we've measured
- Dan Henry 1962 Racing Chronograph DH62-38M-G1
39 mm case · 45.9 mm lug-to-lug · $290
- Swatch Omega x Swatch MoonSwatch Mission to the Moon SO33M100
42 mm case · 47.3 mm lug-to-lug · $300
- Dan Henry 1964 Gran Turismo Chronograph 38mm DH64-38M-E1
38 mm case · 44.7 mm lug-to-lug · $310
- Seiko Prospex Speedtimer Solar Chronograph 39mm SSC961
39 mm case · 45.5 mm lug-to-lug · $750
- Bulova Lunar Pilot Chronograph 43.5mm 98K112
43.5 mm case · 51 mm lug-to-lug · $895
- Omega Speedmaster 38 324.30.38.50.02.001
38 mm case · 44.9 mm lug-to-lug · $6,300
- Tudor Black Bay Chrono M79360N
41 mm case · 49.9 mm lug-to-lug · $6,875
- Omega Speedmaster Moonwatch Professional 310.30.42.50.01.001
42 mm case · 47.5 mm lug-to-lug · $7,800
- Omega Speedmaster Moonwatch Professional (sapphire sandwich) 310.30.42.50.01.002
42 mm case · 47.5 mm lug-to-lug · $9,000
- Omega Speedmaster '57 332.10.41.51.01.001
40.5 mm case · 49.6 mm lug-to-lug · $10,700
- Omega Speedmaster Chronoscope 43 329.30.43.51.02.001
43 mm case · 48.6 mm lug-to-lug · $10,700
- Omega Speedmaster Racing 329.30.44.51.01.001
44.3 mm case · 50 mm lug-to-lug · $10,800
And 5 more in the catalog.
Questions
- What is the formula for a tachymeter?
- Speed = 3,600 ÷ seconds taken to cover one unit of distance. For example, a mile in 45 seconds is 3,600 ÷ 45 = 80 miles per hour.
- Does a tachymeter work for times over a minute?
- Not directly; the scale starts at 60. For longer times, divide 3,600 by the seconds yourself, or time a shorter distance.