In the relative (incremental) positioning mode G91, the position of the actuator, which it occupied before moving to the next reference point, is each time taken as the zero position (it is programmed how long the tool should move). Code G91 is canceled by absolute position code G90.
G90.1 Absolute distance mode for I, J and K offsets.
G91.1 Incremental distance mode for I, J and K offsets.