The BIPM Time Department manages the calibration of time transfer systems used to generate UTC. Calibrations may be carried out by the BIPM, by the RMOs, by individual time laboratories or, in some cases, by other entities such as manufacturers.
Starting 2015, calibrations in laboratories contributing to UTC follow specific guidelines (see GNSS ReadMe, GNSS and TWSTFT guidelines). Calibration results are labelled with a calibration identifier (Cal_ID) to enable the process yielding the results to be traced. The Cal_ID is used to report calibration information in Section 5 of Circular T.
The calibration identifiers are of the form znnn-YYYY
where z identifies the type of calibration;
nnn is a number assigned by the BIPM;
YYYY indicates the year (typically the start of the calibration exercise). The types of calibration are: z = 0: For TWSTFT links, whatever the technique used for the link calibration. nnn then is the calibration identification of the ITU format. z = 1: For GNSS systems, with GNSS calibration campaigns under the supervision of the BIPM; nnn then identifies a report corresponding to a calibration trip; see details in the GNSS Guidelines. z = 2: For GNSS systems, calibrated with other techniques (e.g. manufacturer calibration, absolute calibration, or transfer using a calibrated link); nnn then identifies a report and is a sequential number within the year. z = 3: direct links, e.g. through RF cables or optical fibres; nnn then identifies a report and is a sequential number within the year.
Calibrations made before 2014 have been included in the current scheme by assigning a Cal_ID when a full report is available. The history of calibrations until 2014 can also be accessed at archives .
On this website, you can access the calibration results and reports for all techniques contributing to UTC. Results for time transfer equipment are stored in BIPM Time Department database, some dedicated webpages allow to consult this database .