A chronometer is NOT a chronograph, but a chronograph CAN BE a chronometer. Confusing right? Well, let’s start by defining the terms.
A chronometer is an instrument for measuring time accurately in spite of motion or variations in temperature.
Back in 1714, the British government started the work on chronometers by initiating a contest to find a timepiece that would function accurately on board ships, allowing seamen to calculate longitude. This instrument became known as a marine chronometer (the competition was won by British watchmaker John Harrison).
Today, a chronometer is a watch that has been independently tested (usually by COSC, the Official Swiss Chronometer Testing Institute). The test includes various positions and different temperatures. In order to be tested, a watch has to have a second hand, so its precision can be tested and verified. The COSC standards allow a variation of no more than -4 or +6 seconds per day. Only about three percent of all Swiss watches undergo chronometer certification, though two brands, Rolex and Breitling, certify every movement they use.
Chronometer certification is not cheap, so you expect that chronometers will be more expensive than normal watches, but you can expect them to be more precise, as well.
The Geneva Seal certification recently added a precision test in its testing as well.
A chronograph is a watch that is capable of timing an event independently from its normal timekeeping. Unlike a stopwatch, which only times an event with no normal timekeeping, a chronograph keeps normal time, but let’s you time how long it takes you to get the mail.
Typically, a chronograph has two pushers on the side of its case, one to start the chronograph hand moving and the other to stop and reset it. You read the elapsed time on the watch’s subdials that display minutes and hours.
So, you see, it’s possible to chronometer certify the movement in a chronograph timepiece, but a chronometer is completely different from a chronograph.