The aim of this project is differential verification of short-term and seasonal changes of calibration constants of GPS receivers, including variation due to changes of delays of different parts of equipment. The base method is collection and analysis of measurement data taken from pairs of GPS receivers working with the same local reference timescale, so the data taken from pairs of GPS receivers working with different local reference timescales/clocks, but with supplementary results of direct measurements between the used as a reference timescales/clocks, are accepted.
Theoretically, the difference between GPS receivers in such pairs should be constant, but practically, this difference can vary due to individual sensitivity on external temperature of the equipment, different type of antennas and different type of receivers and software. It is assumed that the data will be collected and analysed for the period of at least one year of permanent observations. The analysis will be performed for GPS C/A code mainly, so with measurement data in CGGTTS format. The involved GPS receivers do not have to be calibrated because the subject of investigations is only the changes with respect to the other one in the pair.