CHRONOGRAPH SCALES EXPLAINED
TACHYMETRE or TACHOMETER: This scale is used for the measurement of speed. Graduations begin at about 1000 at 3 seconds, and go usually to 60 at 12 o’clock..
The graduations can start and stop at other points on the dial, but are always in the same place. This is to say, the dial maker may not put the 1000 on at 3 seconds, but 120 is ALWAYS at 6 o’clock.
Use is as follows: driving in your car, start the chronograph sweep second hand at a mile marker. When you get to the next mile marker, stop the chronograph.
The chrono sweep second hand is now pointing to your speed for that mile: 40 seconds = 90 miles per hour, 51 seconds = 70 miles per hour. This is the most common chronograph scale, and the most useful.
TELEMETER: Speed of sound measurement. If in Miles, this will be a scale around the dial with 12.5 at 12 o’clock, if in Kilometres it will have 20 at 12 o’clock.
Based on an average speed of sound of 333 meters per second at an air temp of 10 degrees Celsius, this scale works like this: Start the chronograph when you see the lightning flash, and stop it when you hear the thunder boom. Three seconds means that the lightning struck one kilometre away.
This was used extensively in the 40s chronographs for measuring artillery rounds. Remember that speed of sound varies considerably with temperature differences, so this scale is not hugely useful.
PULSE REGISTER: Common on so called "Doctors Watches." Will usually say, "Gradu Pour 15 Pulsations", or something similar. The scale (for 15 pulses anyway) will say 90 at 2 o’clock, 60 at 3 o’clock, 30 at 6 o’clock, etc..
The doctor or nurse who needs to know your heart rate, rather than counting for a full minute, or counting for 15 seconds and multiplying by four, will just start the chronograph, count 15 heartbeats, stops the chrono and reads your pulse rate without all that annoying and difficult multiplication.