From CoMakingSpace Wiki
|Material:||wood and engineered woods|
A marking gauge is used to scribe a line that is parallel to the workpiece's edge. That is often useful to transfer the center line of a hidden piece for suitable screw positions or the depth of cuts for various joinery techniques, for example.
A quick and dirty marking gauge can be made from a sharp-edged screw and a piece of scrap wood (see photo on the left). The distance from the guiding edge can then be adjusted by turning the screw. 
Some marking gauges have a cutting wheel instead of a scriber.