Most commercial machines, Mach is included in this, use two co-ordinate positions, Machine Co-ordinates [ MC ], are set at the homing switches and are just used for this purpose.
Knowing where home is every time means that you can set soft limits accurately so you can't run off a table.

Once homed and MC set for the first time it can be forgotten.

You then switch to Work Co-ordinates [ WC] and this is where you set the corner of your work or vise etc.

A goto zero command will return the tool to this position, a goto home command will send it back to the homing switches.

Mach can use two switches per axis daisy chained together and connected to one input, either switch can be designated as the home switch so for example you can have the tool home at the far right or far left of the bed, your choice.

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