Inspired by Trobinou's combination square (https://www.thingiverse.com/thing:1905410). I redesign the tappered parts so that they are printable. Four additional M3x0.5 10mm bolts and nuts are required to fix them on base. The ring to hold bubble level is also redesigned so that it is easier to be printed.

The usage is simple: Rotate the printed bolt counter-clockwise to release ruler for movement. Move the ruler to the target location and then screw the bolt clockwise to fix the ruler. Notice that the four M3 bolts can be used to adjust the force to hold the ruler.