G90 Absolute Positioning. Moves are to an imaginary grid centered at X0 Y0 Z0. Modal, it stays in effect until canceled with G90.1 or G91. Modal, it stays in effect until cancelled with G90 or G91. G91 Incremental Positioning.
Moves are from the current tool location.
This command is modal, it stays in effect until canceled with G90. I, J, and K will be incremental. G92 Relocate Absolute Zero. Relocates the origin to a point X, Y, and Z away from the current tool location. The G92 command MUST be on a separate line.