Making accurate angle cuts on a horizontal bandsaw can be a bit tricky if you don't have, don't trust, or need more precision than the gradiated presets provide. This is the technique I use.
Step 1: Safety First
FIrst things first, make sure emergency stop is depressed and the feed rate is set to zero. Both of these should be set anytime you're manipulating the machine. Don't take any risks.
Step 2: Adjust Moveable Vise
Loosen the nut on the moveable vise face, place a protractor against the fixed face, rotate the moveable face to the desired angle, and retighten the nut. It's easier to move the vice face than the whole bed and this way you don't have your face in the machine.
Loosen both bed brakes. It turns out it's possible to rotate the bandsaw with just one brake loose, but it's a bad idea and really hard. I found out from a guy I know.
Rotate the bed until the fixed jaw is approximately parallel with the moveable jaw, place a piece of flat stock between them and tighten the vise. This will rotate the bed until the faces are (near) perfectly parallel. Re-tighten both brake levers and make your cut.
A half-degree? I can live with that.
I made it (this instructable) at the TechShop (Menlo Park).