I think industry standard is that G53 is the machine's coordinate system. G54 is the first work offset. I don't know if Mach follows this convention or not?
When you home the machine, that sets the machine zero of the G53 coordinate system. This is actually the only 'real' coordinate system that there is, all the work offsets are relative to the G53. Whatever values you see in your work offset tables are actually coordinates in the G53 coordinate system. The G54 through G59 coordinates are the location of a temporary shift in position of the current part's coordinate system origin from machine 0,0,0 to that newly named position.
First you get good, then you get fast. Then grouchiness sets in.
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