Put in your corner and your crown. Get the saw settings — and a picture of exactly how the piece sits on the saw.
Most corners are not really 90°. Measure yours — Step 1 below shows how.
The spring angle is measured from the wall. On 52/38 stock it is 38°, not 52°.
52° spring is chart-verified at square corners; other corners use the same verified formula.
Use an angle finder or protractor on the corner if you have one. A corner that looks square is usually not: framing is rough and drywall mud builds up in the corner, so a "90°" corner often measures 88° or 92° — and crown shows every degree of it.
No angle finder? Use two tape measures. Mark the same distance from the corner along both walls — 24 inches works well. Measure straight across between the two marks, then work out the angle:
The presets above cover most stock: 52/38 crown is a 38° spring, 45/45 crown is 45°. To measure an unknown piece, sit it in a framing square exactly as it sits on the wall. Measure the height (the ceiling side, vertical) and the projection (the wall side, horizontal — how far it sticks out from the wall).
Set the miter and bevel shown in the picture above, and place the piece the way the picture shows it — which edge is at the fence, which side of the blade to stand on, and which end is the long point. The picture changes when you change the piece or the method.
Pros test on scrap; one test cut is cheaper than one ruined stick. Cut two short pieces, hold them in the corner, and check the joint before you cut good stock.
Angles are figured from your measurements — always test-fit on scrap before cutting good stock.
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