There are service ports covered with plugs in the side of each sterilizer chamber (2 on the SN/SQ and 1 on the SM). These are shown on page 12 of the SN/SQ service manual and on pages 4, 23 and 32 of the SM service manual. These are the ports used to insert calibration and temperature recorder probes.
For calibration, you only need to measure for temperature since pressure readings coincide with temperature, as can be seen in the table shown on page 37 of the SM service manual.
The SN/SQ sterilizers have an calibration offset function you can use to compensate for any temperature variances you find. The SM does not have this function and can only be brought back into spec by replacing the temperature control circuit (including heater and sensors). You can also try adjusting the position of both the calibrator probe and sensor to try and bring the calibrator and control panel readings more in line with one another.
It would probably be a good idea to do a little testing and experimentation with the machines at YSA before attempting any onsite customer calibrations.