The most useful tool I've added to my shop in months is a red plate full of holes.
The most useful tool I've added to my shop in months is a red plate full of holes. It's a marking ruler. Hook the T-end over the edge of a board, drop a pencil into the numbered hole you want, slide. You get a line perfectly parallel to that edge, at exactly that distance, in one pass — no measuring at two points, no straightedge, no line that quietly drifts. The catch: the holes run diagonally in single-millimetre steps, so counting into the wrong row puts your line 4mm off. Nothing looks wrong about it until the part doesn't fit. Full write-up in the wiki — link in bio.