Marking gauge

[2] The purpose of the gauge is to scribe a line parallel to a reference edge or surface.

The gauge consists of a beam, a headstock, and a scribing or marking implement, typically a pin, knife, pen or wheel.

Generally speaking, the pin and knife yield more accurate marking than do the pen or pencil.

Other variations include a panel gauge which has a longer beam and larger headstock for scribing lines that are further from the reference edge.

This gauge is used to scribe two lines simultaneously and is most commonly used to lay out mortise and tenon joinery.