How to Use a Chronograph

Chronographs were originally used for horse racing and aviation, but then expanded to automobile racing as well as naval and submariner natviation. Using a chronograph is actually very simple. The confusing part is understanding how to determine how the information is useful.

Photo by @timevaluestl

In the early 20th century, manufacturers began selling watches with a fixed bezel to operate as a Tachymeter, or a scale that allows the wearer to compute a speed  based on travel time or measure distance based on speed. So, you start the chronograph and once the desired distance has been reached, the point on the scale that lines up with the second hand indicates the average speed reached while traveling this distance.

The subdials keep track of seconds, minutes and hours. On most chronographs, you start the chronograph hand by pressing the button at 2 o’clock. Stop it by pushing that button again. The button at the 4 o’clock position is to reset the chronograph.

The formula to measure speed is T = 3600/t. T is the numbers on the tachymeter scale; t is the time in seconds measured by the watches chronograph function for the event to happen. 3600 is the number of seconds in an hour. For example, if it takes you 30 seconds to travel one mile, the corresponding number on the tachymeter is 120.

T = 3600/t

120 = 3600/30 which translates to traveling 120 miles per hour

To measure distance, you have to know the speed at which you are traveling, which can be determined by your chronograph as shown above. So, if you are traveling at 120 miles per hour and you have traveled for 45 minutes, you can determine the distance by

120 miles per hour/60 minutes per hour = 2 miles per minute

2 miles per minute * 45 minutes = 90 miles

Photo by @rolexdiver

There are multiple chronograph variations dependent on the different demands. The Rolex Daytona is a standard chronograph. The chronograph hand takes the place of the second hand, and the second hand operates on the sub-dial at the 6 o’clock position.

Another chronograph is called the flyback. The flyback allows the second hand to be rapidly, stopped and restarted, and reset. When the chronograph hand is stopped and then restarted, it will start from the spot where it stopped. The sweep seconds hand can quickly “flyback” to zero when the pusher is pushed which means there is a much quicker reset.

The rattrapante, or split-seconds, chronograph is a more expensive chronograph with a much more complicated movement. It is most useful when timing multiple events that start at the same time but may not end at the same time. The chronograph and split-seconds hand can be stopped and started independently. Press the pusher to stop the chronograph hand at the end of the first event, but the split-seconds hand continues to time. After recording the desired amount of time, press the pusher again and the chronograph hand will catch up to the split-seconds hand as it continues to move around the dial.

Chronographs are useful for more than just race car drivers or pilots. They can be used for any project that requires a calculation of time; in other words, anything that requires the use of a timer. They are simple to use and yet, can become very complicated to read dependent on the model.