This is a edge line guide tool. There are holes at every quarter inch and two additional subdivisions on top of that. Marks on the bottom identify every quarter inch. Place a pencil in the desired hole, then run along the edge of a board to get a parallel line at the exact distance you want.

Simple and easy to use, great way to get a line at a fixed distance from any edge.

I did a textured PEI plate, so the diamond pattern on the surface comes from that. The print is done face down so that the text will be flat and only have minimal filament changes.