KB001870: If the Highest Tuning Mass is 502, What are the Steps to Make Mass Assignments at 1050? - MS ChemStation 

All most all the manufacturers calibrate their instrument with perfluorotributylamine (PFTBA). Instruments are calibrated to 502 u and extrapolated from that point. Agilent is unique in providing a high mass test kit to verify that the mass assignments at the high end are correct. Deviations are noted in the report and the proper voltage changes listed.