A chronograph is a watch with additional short-time measurement (stopwatch), shown by an additional hand (chrono hand) which can be started, stopped, and reset to zero by pushers in the housing wall.
Most chronographs feature one or more hands on a dedicated dial or subdial to show recorded seconds, minutes, and hours. These are often referred to as totalizers, recorders, or registers since they keep track of elapsed time.
It is critical that the various wheels that control a chronograph are synchronized. There are two methods currently in use to accomplish this One where the chronograph function is controlled by a column wheel, the other with the control function by a coulisse lever system (also slotted lever shift or cam switching).
Traditional chronographs engaged and disengaged the chronograph wheels using an oscillating pinion, a simple lever which drove the gear teeth together. This abrupt system was effective but problematic, since it was possible for the gear teeth to be damaged over time. It also caused issues with timekeeping, since engaging the chronograph could reduce the amplitude of the movement.
A more elegant system of engagement uses a vertical clutch, similar to the type found in automobiles. This is a more complex solution and demands greater precision of manufacture but has the benefit of smoother engagement and disengagement of the chronograph mechanism and less interference with the timekeeping wheels. For this reason, many advanced and upscale chronograph movements use a vertical clutch.
Most chronograph watches use two buttons The top (at 2 00) starts and stops the chronograph counter while the bottom (at 4 00) resets the counter to zero. Some (including the Landeron calibres 48, 51, 148 and 248) use the bottom button to stop and reset with the top only starting the operation.
Some early chronographs, and a few modern homages, use a single button. These so-called monopusher chronographs use a single button to start, stop, and reset the chronograph function in sequence. A range of “timer” watches from various brands are examples of modern monopusher chronographs.
Today even many watch fans don't know that it is only since the year 1969 that chronographs with automatic winding have been manufactured. The race to develop an automatic chronograph included two Swiss/American groups Heuer/Breitling/Dubois Dépraz/Buren/Hamilton with their microrotor Chronomatic, and Zenith/Movado with their high beat central rotor El Primero. Seiko also brought their own automatic chronograph to market at the same time.
Probably the most successful automatic chronograph movement ever built is the proven and robust calibre Valjoux 7750 by ETA, which is built into most of today's mechanical chronographs in many variants. Other well-known movements are the (no longer produced) Lemania 5100 and the in-house Rolex manufacture movement 4130. Many high-end Swiss manufacturers produce their own such movements today.
The measuring accuracy of chronographs depends directly on the oscillation frequency (amplitude) of the movement and of the balance wheel.