With the instructions G90/G91, the written positional data X, Y, Z, ... are evaluated as a coordinate point (G90) or as an axis position to traverse to (G91). G90/G91 applies to all axes. Irrespective of G90/G91, certain positional data can be specified for certain blocks in absolute/incremental dimensions using AC/IC. These instructions do not determine the path by which the end points are reached; this is provided by a G group G90 ; Absolute dimension data G91 ; Incremental dimension data X=AC(...) ; Absolute dimensioning for a certain axis (here: X axis), non-modal X=IC(...) ; Incremental dimensioning for a certain axis (here: X axis), non-modal See the following illustration for different dimensioning types in the drawing:

Absolute dimensioning G90

With absolute dimensioning, the dimensioning data refers to the zero of the coordinate system currently active (workpiece or current workpiece coordinate system or machine coordinate system). This is dependent on which offsets are currently active: programmable, settable, or no offsets. Upon program start, G90 is active for all axes and remains active until it is deselected in a subsequent block by G91 (incremental dimensioning data) (modally active).

Incremental dimensioning

G91 With incremental dimensioning, the numerical value of the path information corresponds to the axis path to be traversed. The leading sign indicates the traversing direction. G91 applies to all axes and can be deselected in a subsequent block via G90 (absolute dimensioning).

Specification with =AC(...), =IC(...)

After the end point coordinate, write an equality sign. The value must be specified in round brackets. Absolute dimensions are also possible for circle center points using =AC(...). Otherwise, the reference point for the circle center is the circle starting point. N10 G90 X20 Z90 ; Absolute dimensions N20 X75 Z=IC(-32) ; X-dimensions remain absolute, incremental Z dimension N180 G91 X40 Z20 ; Switch-over to incremental dimensioning N190 X-12 Z=AC(17) ; X-remains incremental dimensioning, Z-absolute