Peter James replies: I assume that the question refers to tuning the saw to make straight and square cuts. The key is to have everything in alignment. The alignment should be done in reference to the left miter gauge slot.
First align the blade and arbor by selecting a tooth on the blade that is tipped or set towards the left slot. Mark it with a marker or pen. Measure the distance from the tooth to the slot using a dial indicator or other accurate measuring device with the tooth at the front of the blade opening. Then rotate the blade so the tooth is at the rear of the opening. Measure the distance again. If there is a difference, adjust the trunnions until the measurement is the same in both locations. Now adjust the fence to the left slot using the same accurate measuring device. I like it dead on parallel to the slot, but some prefer to have it open slightly from front to rear, no more than 0.005˝.
The stops for the blade angling should be checked using an accurate square. It is easier to make a cut and measure the cut than to try to measure the blade because the blade may be taper ground and not flat. Adjust the stops and indicator strips when you have made cuts that are square and also 45°.
This was covered in an article I wrote in The Old Saw (June, 2006) www.gnhw.org