Chronometer : The label given to a precision timekeeping instrument set for various conditions of use (e.g. ISO 3159 for mechanical wristwatch).
Chronograph : A timekeeping instrument with a counter for measuring and displaying time intervals irrespective of the conservation and possible indication of time. It may also include a recording device.
A chronograph alone cannot be certified a chronometer, as the function of a chronograph is to measure short times - the duration of a particular event. At present, there is no standard to certify the precision of a chronograph. On the other hand, high precision watches with a chronograph function can be certified as chronometers.