I have been told (by “Moltke” at the HDD Oracle) that the checksum is automatically recomputed by the drive before the MOD is written to the platters. Therefore there is no need to bother with it. The only time you need to take it into account is when you are writing the module in CHS mode.
BTW, last night I confirmed that my understanding of the VSC was correct by retrieving a different section from MOD 02 in an earlier pre-ROYL model using an MHDD script.
