Chronograph and Chronometer - what's the difference?

A Chronograph is a timepiece equipped with additional time measurement functions independent of normal time-telling. It is also known as a stop-watch.

A Chronometer is a high-precision timepiece which movement, after rigorous testing, has received an official timing certificate from and official timing bureau.

Watches providing additional measurement functions to the hours, minutes and seconds are referred to as "Complications". The best-known complication watches are calendar watch, the most common of which display only the date. There are also chronographs with a center seconds hand which can be started, stopped and brought back to zero using one or two push-button on the side of the watch. Other additional functions include second time zone, alarm, moon phase, repeater, perpetual calendar, etc.