{"id":"gcode-g90-1","model_id":"G90.1","name":"LinuxCNC G90.1","summary":"G90.1 selects absolute arc distance mode in LinuxCNC, so the I, J and K arc center offsets in G2/G3 blocks are measured as absolute distances from the current 0 position of the axis rather than from the arc start point. In this mode both offsets for the active plane must be programmed: I and J for the XY plane, or J and K for the XZ plane. Incremental offsets, which are the default, are restored with G91.1.","study_notes":["Arc center offsets in absolute arc distance mode are the absolute distance from the current 0 position of the axis.","For arcs of less than 360 degrees, one or more axis words and both offsets must be programmed.","For full circles, no axis words and both offsets must be programmed; the P word defaults to 1 and is optional.","Incremental arc distance mode (G91.1) is the default; G91.1 returns I, J and K to their default behavior.","Center format arcs using I, J and K offsets are more accurate than radius format arcs and are the preferred format."],"safety_notes":["Programming G90.1 without both required offsets for the active plane (I and J in the XY plane, J and K in the XZ plane) with G2/G3 is an error."],"sources":[{"url":"https://linuxcnc.org/docs/html/gcode/g-code.html#gcode:g90.1-g91.1","title":"G-Codes","accessed":"2026-10-26"}],"verification":{"status":"source_checked","checked_at":"2026-10-26","values":3,"method":"llm_source_check"},"updated_at":"2026-10-26","type":"instruction","spec":{"language":"gcode","code":"G90.1","group":"Arc Distance Mode","syntax":"G90.1","parameters":[],"dialect":"LinuxCNC","related":["gcode-g02"],"standards":[]},"url":"https://machineschema.com/instruction/gcode-g90-1","license":"https://creativecommons.org/licenses/by/4.0/"}