This is a tool I printed up for Military personnel who need to make sure that devices are placed on their uniform at the correct spacing. Sure, a ruler would work, but this fits on a keyring! And it's printable! The tool includes 1/4, 1/2, 3/4, 1, 1-1/2 and 2 inch features. (the 1, 1-1/2, and 2 inch features are on the back side)
Note: if you're senior enlisted, don't use this for inspections. Your calibrated eyeball is plenty good enough. ;) Not to say that this tool is inaccurate. It isn't inaccurate. I just don't want to be the source of more pain.
I printed this in two colors by manually inserting an "M600" command in the gcode when I wanted to change the filament manually. For those of you lucky enough to have a dual-head (or better), let me know in the comments, and I'll figure out how to make a dualstrusion model.