To calibrate the chromatic response, observations of a standard star (preferably more than one) are needed, for which the absolute fluxes are known. The spectral response curve of the instrument can then be determined with the command RESPONSE/LONG, and absolute fluxes for the objects of interest are obtained with CALIBRATE/FLUX. The extinction correction must previously be done in a separate step with the command EXTINCTION/LONG.
An alternative procedure, if no standard star spectrum is available, is the normalisation of the continuum as described below.