I too have the foremost miter sander......it does an excellent job.

The balsa rests against the black arm and the arm rotates to the angle you want to sand to. The sanding block fits in a groove and slides back and forth in that groove.

The only thing I dislike about it is that the sanding block is fairly small and if you use it alot, your hand cramps up from hold such a small block. COULD EASILY MAKE A NEW BIGGER ONE!