Step 5: Cutting the dovetail angle
Take the dovetail guide and align it to the groove on the top of the base. Do this by taking a chisel and placing it at one end of the base, along the groove, and sliding the guide up to it, then doing the same thing at the opposite end. Keep adjusting until the guide is right in line with the groove, then clamp down. Test again after clamping, because sometimes the clamping gnomes will sneak in and move stuff around, because they're little jerks like that.
With the guide in place take your largest chisel and, starting at one end of the board, remove the waste inside the groove. Use the guide to keep the desired angle. Keep the bevel of the chisel toward the groove. Because you are chiseling with the grain, this should require little effort. However, if you come across a nasty spot in the wood, carefully use the wooden hammer to persuade the wood to come out and play.