Calibrate your miter gauge, part I
To ensure that your miter gauge squares with the blade, try this trick: Set it for a 90° cut and then crosscut one end of a 6" (or wider) scrap. Flip the scrap top-for-bottom, keeping the same edge against the miter gauge, as shown, and repeat the cut at the other end of the scrap. Now, compare the lengths of the two edges of the scrap using a precision steel rule. If A and B match exactly, the miter gauge is square. If not, adjust the gauge and repeat the test cuts until they are, and reset the cursor.