The effective frequencies and half-power beam-widths for the filters, and the brightness temperatures for the planets (except Mars) are read from the plain text files:
The information in the files was supplied by the observatory. The differences mainly reflect changes in detector/telescope hardware.
The program selects the appropriate .dat file to use, based on the date you specify. The calculated temperature has an rms error of about 0.13K (negligible).
Bear in mind that Saturn can only be used for calibration when the
rings are not open, and the Martian brightness temperatures are probably
only accurate to around %.
FLUXES JCMT Position and Flux Density Calibration