The SPI instrument has been fully tested and calibrated on ground. Soon after the launch the observations of the Crab nebula and Cygnus X-1 were done for further calibrations.
The detector gains, thresholds and resolution versus energy are determined from normal event data and ACS off spectra (for consistency checks) in the routine monitoring task at ISDC. In addition, after every detector annealing a thorough check is done of the instrument imaging and spectroscopic response, since these may change as a result of the annealing process.