How Chronographs Actually Work

Vintage Rolex Daytona Stainless Steel 6265 FAP

Maybe the most common complication found in a wrist watch today, besides a date function, is the slightly anachronistic and slightly misnamed chronograph. A working definition of a chronograph is simply a watch with the capability to time events of short duration (elapsed time), while also keeping the time of day (which we'll call conventional time).
The word chronograph literally means time writer. The name was apropos back when timers actually recorded elapsed time using a pen held against a moving sheet of paper.

Rolex 6236 Triple Calendar Chronograph

Nowadays, of course, nothing on your typical chronograph actually marks down the elapsed time. Rather, the operator sees it temporarily indicated on sub dials. Thus, a more accurate name for the timer is 'chronoscope.' A few brands have acknowledged this, Gerd R Lang's Chronoswiss being one of them.
Now we won't quibble over a name, but just how do these 'time writers' actually work?
The elapsed time of short duration events, usually up to 12 hours (racing laps, scientific experiments, cakes baking in the oven, coffee brewing), is tracked on sub-dials which separately record minutes and hours. Seconds are commonly measured on a central sweep seconds hand. (The running seconds for conventional time is typically located on a sub-dial.)

Rolex Chronograph 6234

Basically, the chronograph portion of a watch movement has to tap into the power and timekeeping portions of the regular watch mechanism. As such, it may be a separate module riding on top of a conventional movement, sandwich style. Or it may be incorporated into the movement itself.
As you can guess, very quickly we get into enough permutations that this article could be a book instead. So we'll narrow our look to integrated movements.
You can think of the Start/Stop pusher of a chronograph as the button that connects and disconnects the chrono mechanism with the conventional mechanism. The mechanism can do that in either of two ways. It can move the elapsed time gearing vertically to engage with the conventional timekeeping mechanism, or it can move the gearing horizontally (here, 'vertical' and 'horizontal' refer to up/down and 'from the side,' respectively, when the movement is lying flat on a table).

Movement Rolex Chronograph 6234

The way the mechanism keeps track of where it is in the timing cycle is by means of either a column wheel or a system of a cam and levers. The column wheel looks a bit like a castle turret – a flat gear with a number of columns rising off one side which engage with the mechanism to control its function.
The cam and lever mechanism, on the other hand controls the chrono mechanism by the orientation of the heart shaped cam.

Rolex Anti-Magnetic Oyster Chronograph 5034

As we noted above, the Start/Stop pusher engages and disengages the chronograph mechanism. Then, when the mechanism is disengaged and the operator wants to zero the chronograph, he pushes the Reset pusher. In a column wheel mechanism, the column wheel activates a finger which zeros the chrono hands. Similarly, with the cam/lever mechanism, the cam is forced to a 'home' position which zeros all chrono hands.
Note what we said: the operator pushes the Reset pusher when the mechanism is disengaged . However, with one unique type of chronograph, the operator can activate the Reset pusher and have the chronograph reset while it is running . This is called a flyback chronograph, and it's useful for timing consecutive events back to back.

vintage rolex daytona 6265

Another type of chronograph is the split seconds chrono. This version has two sweeping chrono seconds hands. One is able to be stopped with an auxiliary Start/Stop pusher. This will allow the user to record the intermediate time, before activating the auxiliary pusher again to allow the stopped hand to instantly catch the other chrono seconds hand, which is still running.
Finally, we'd like to note that the majority of chronographs today are of the cam and lever type, as it's easier to produce. Some feel, however, that the cam and lever is not quite as precise as the column wheel. Thus, a notable exception to the cam and lever camp is Rolex's 4130 chronograph movement which powers the modern Cosmograph Daytonas. The 4130 uses a column wheel, along with a vertical clutch.
Just one more detail that sets Rolex apart.

vedere di piu rolex e Rolex Sea Dweller