As far as I am aware, calibration can only be carried out by Rivertrace as part of a laboratory procedure. However, Rivertrace do provide a calibration verification fluid under part number 107651 that can be used by ships staff to prove that the monitor is still within calibration limits. The fluid has a limited shelf life of some two weeks and so has to be ordered immediatly before use. If the unit fails this then it should be returned to Rivertrace for full calibration.
I suggest you contact Rivertrace and ABS again to see if this is a suitable solution.