Technical: Chronograph

Clocks and watches were used, are used and always will be used to display the never-ending movement of time. But say you're an avid fan at the 1821 races and you need to know precisely how long it is between the horses leaving the start line and crossing the finish line, what then? Oh, and you're Louis XVIII, King of France, too. I’ll tell you what you do. You commission the invention of the chronograph.

A working chronograph already existed, made in 1816 by Louis Moinet, but he was an academic who used it for private astronomy. So it was inventor Nicolas Rieussec who took the credit for the invention when he presented his version to Louis XVIII. He called the device a chronograph, a word formed from the Greek for ‘time’ and ‘writing’, because it literally wrote on the face of the clock. When started, a needle deposited a drop of ink that was dragged around the face, recording the elapsed time.?

It was Moinet’s concept—a device that used additional hands to record time—that worked best, but it was Rieussec’s moniker—chronograph—that stuck. The chronograph was improved in 1844 when a reset system was introduced by Adolphe Nicole; Joseph Taddeus Winnerl’s rattrapante (split seconds) complication followed in 1870, allowing two events to be recorded at the same time. Tachymeters were added to assist the calculation of speed, and rotating bezels and chapter rings with printed slide rules catered for more intricate computation. The chronograph had found a home—multiple in fact—on the wrists of scientists, engineers, pilots, drivers, sportsmen and even astronauts.?

Because the chronograph is so prolific it is often misunderstood to be a simple complication, but that couldn’t be further from the truth. The principle issue to overcome is the coordination of the different operations—start, stop and reset—in such a way that doesn’t grind the movement to a halt. A peek at the layers of gears and levers in even a simple chronograph is enough to convey just what an undertaking that is.

The chronograph is driven from the power and beat of the base movement onto which it is built. For a simple chronograph, only two pushers are needed: one for start and stop, one for reset. The first pusher actuates a lever that rotates either a column wheel (a wheel that looks like a castle’s turret) or a heart-shaped cam. They both work in similar ways, with the column wheel being the more precise but difficult to manufacture of the two. When the column wheel is rotated, another lever dips into the gap between the columns, moving the clutch wheel that provides the drive from the base movement against the chronograph seconds wheel. The chronograph minute and hour wheel, through a train of gears, are also engaged. To stop is the reverse: press the pusher and the column wheel rotates again, the column forcing the clutch wheel away and removing the driving force to the chronograph wheels. The lever also engages a brake to keep the chronograph wheels in place. Reset is straightforward, with the pusher driving three hammers that force heart-shaped cams on each chronograph wheel back to their original position. The column wheel serves a final purpose here, blocking the reset button when the chronograph is running.

The more complex chronographs add even more trickery to the movements, but their core is still the same. It’s a complication that’s made and broken records, timed historical events, even saved the crew of Apollo 13—oh, and it probably made King Louis XVIII a tonne of gambling money, too.