Conformity with the definition of a chronometer is accredited by a neutral official body which checks the movement and issues an official certificate. In Switzerland, each chronometer is unique, identified by a number engraved on its movement and a certificate number supplied by an independent laboratory (COSC or Timelab).
The term "chronometer" is often incorrectly used to describe instruments designed to measure short time periods and whose mechanism is activated by a push-button. Such an instrument is in fact a chronograph or a chronoscope, while a chronometer is a high-precision timepiece.
For the LONGINES ULTRA-CHRON (Calibre L836.6), Longines went a step further in submitting the entire watch head to Timelab for chronometer certification. The entire watch, once the movement was cased up, was tested over 15 days in line with the ISO standard 3159. An added guarantee of excellence.
CHRONOMETER
The label given to a precision timepiece set for various conditions of use (in line with the ISO standard 3159 for mechanical chronometer wristwatches).
CHRONOGRAPH
A timekeeping instrument comprising a time counter for measuring and displaying intervals of time independently of the timekeeping and the time display. It may also include a recording function.
Certification
Timelab
COSC