What function does the "G91" command provide?

The "G91" command is significant in CNC programming as it sets the machine to incremental positioning mode. When this mode is activated, all movement commands following "G91" are interpreted as incremental movements based on the current position of the tool rather than from a fixed point in the coordinate system. This means that if a command specifies a movement of a certain distance, the tool will move that distance from its current location rather than from an absolute coordinate.

This incremental approach can be particularly useful for programming certain parts or operations where you want to perform movements relative to the last position rather than a defined origin. It allows for more flexibility when making multiple moves in a sequence without needing to constantly redefine or calculate absolute coordinates.

In contrast, absolute positioning mode, which is established by the "G90" command, requires that all movements are referenced from a fixed origin or starting point. The other choices provided do not pertain to the specific function of "G91."