Zero offsets are modal. Command positions programmed after programming zero offsets, are referred to the new origin. In case it is necessary to refer a position command with respect to machine zero, suppressing the programmed zero offsets, then the code G53 is programmed. G53 is block wise active. i.e. it can suppress zero offsets only in the block in which it is programmed.
G53 Code Example
N5 G55 ; Activates the zero offset already loaded in the zero offset memory G55.
N10 G00 X100 Z200 ; Command position is with respect to new origin.
N50 G53 X100 Z200 ; G53 suppresses zero offset G55, and command position is with respect to machine zero.
N55 X100 Z200 ; Command position is once again with respect to G55 zero.
In case of touch probe, G53 is used for automatic tool offset entry in JOG MODE, and automatic updating of already entered tool offsets in AUTOMATIC MODE (by executing a special program, where all command positions are to be defined with respect to machine zero).