@Kinch, SGP is writing the fit headers so it can write the RA/Dec values from the plate solve rather than what the mount says. I don't know exactly how SGP does it now but the sync does not guarantee the right RA/Dec values. It only (potentially) matches the mount values to the plate solve but then SGP does a correction slew so the mount RA/Dec values no longer matches the plate solve. So the sync does not assure the right mount values in any case. It is an interesting point you raise. With either method, SGP has to do some work to get the right RA/Dec values in the fit's header.
There seems to be some misunderstanding about what I am proposing.
Currently, SGP does:
1. Slew to desired location; take a picture; do a plate solve
2. Sync the mount to the plate solve location and again slew the mount to the desired location.
Within the mount, the second slew has the effect of slewing to the delta between the plate solve and the desired location.
What I am proposing is:
1. Slew to desired location; take a picture; do a plate solve
2. Within SGP calculate the delta between the plate solve and the desired location. Add that delta to the current mount position and slew to that location.
Except for math differences, the second slew goes to the same location, however, the mount has not been sync'ed.
What I don't know is whether in some mounts the sync does some magic to account for built in mount errors. That is why I propose testing on different mounts to uncover any such issues. Ultimately, Jared and Ken will have to determine what priority they attach to the sync problem on some mounts and whether it is worth fixing.