Set incremental distance mode.
In incremental position mode commanded moves are interpreted as distance and direction from the current position.
G91 is a G-code used to set the distance mode to incremental. It means that all coordinates are given in reference to the machine's current position. With the G91 mode, the machine will move to a position relative to its current position, rather than to a specific absolute coordinate.
For example, if a G-code program has the command G91 G0 X10 Y5 Z0, the machine will move 10 units in the positive X direction, 5 units in the positive Y direction, and 0 units in the positive Z direction from its current position.
G91 is used in contrast with G90, which is used to set the distance mode to absolute. In absolute mode, the machine will move to the exact coordinates specified in the G-code program regardless of its current position.
G91
G91