Check Miter Saw Calibration With a Speed Square — Then Reset the Scale to Match

The Problem

Miter saws leave the factory calibrated. Then they get loaded into trucks, jostled across job sites, and occasionally dropped — and nothing about the saw tells you it's no longer cutting square. You find out from a miter joint that won't close.

There's a second, sneakier version of the same problem: even after you've squared the blade, the printed miter scale may no longer agree with it, so the saw cuts a true 90 while the pointer sits somewhere other than zero.

The Technique

1. Extend the blade fully — pull the saw head all the way out on its slides — before checking anything. A blade that reads square at one point in its travel can drift across the rest of it.
2. Set a 12-inch speed square against the fence and the blade. The longer edge is doing real work here: a short square can sit flush against a blade that's meaningfully out over a full cut. Look for daylight between the square and the blade body.
3. Adjust the blade to the fence with the saw's own adjustment until the square shows no gap, and lock it down.
4. Re-zero the scale. Loosen the screws holding the miter scale, shift it slightly so the zero mark and the red indicator arrow line up with the saw in its now-true position, and retighten.
5. Repeat the square check to confirm nothing moved while you were tightening.