GETMEASUREMENTS [COORDINATE &stem/.HORIZONTAL.VERTICAL][RELATIVE
&rmsys][TEXT &tmsys] [FROM &from<PAGE|SPREAD>]

Just make sure that if you get SAMEAS for vertical, relative, or text
coords that you don't pass that to the GetGoord/GetString calls, but
instead substitute the horizontal measurement system returned.

The coord is a large interger number than you can add together, divide,
etc. If you want to add say 1 inch to something, then you would simply need
to pass "1in" to GetCoordFromString to get the number to add to the coord.
Then if the PageStream numbering system ever changed, you're "future proof".

GetCoordFromString
GetUIStringFromCoord
GetCmdStringFromCoord