Reader Dave Willis, of Murray, Utah, shares his simple method for truing up your miter gauge using a scrap of MDF and a square.
Accurate Miter Gauge

A tablesaw tune-up article in a recent WOOD magazine inspired me to share a simple and accurate way I use to true my miter gauge to 90 degrees. Begin with a scrap of 3/4" sheet goods—I prefer medium-density fiberboard (MDF)—at least 8x8" that has one perfectly straight edge. Mark this edge as 1. Label the other edges 2, 3, and 4 in a counterclockwise direction (as shown in the drawing, above). Place edge 1 against your miter gauge set at 90 degrees and cut edge 2, then rotate the piece clockwise and repeat for edges 3 and 4. The three cuts will cause any angular error to be magnified by three because each cut adds to the error of the previous cut. Using an accurate square, check the angle between edges 1 and 4 for square. If a gap shows on the inside elbow of the framing square, adjust the miter gauge counterclockwise; if the gap is at the top of the test piece, adjust the gauge clockwise.
-Dave Willis, Murray, Utah