To get an accurate crosscut on the table saw, the blade has to be parallel with the saw's mitre gauge slots. A quick way to check this is to use a combination square and a marker, see top photo below. If your blade isn't parallel to the mitre gauge slots, the table saw trunnion needs to be adjusted. (The trunnion is the assembly that holds the saw's arbor to the underside of the saw table.) Normally, all you need to do is loosen the bolts that hold the trunnion and tap the trunnion in the direction needed.
MARK TOOTH To check that your blade is parallel with the mitre gauge slot, first mark a tooth. Then place a square in the slot and adjust it so the end of the square just touches the side of the marked tooth.
ROTATE SAW BLADE Next, slide the square and rotate the blade backward until the marked tooth aligns with the square. If the square just touches the side of the tooth, the slot and the blade are aligned.
Ted's Woodworking - Guide eBook