SplinterGroup
 commented about 6 hours ago
new
So, that turny-knobby thing is a ovoid vernier to adjust your angles? 

That thingy is used to lock the two rulers (through the appropriate holes) at 90° when the apex is off the board.  After RTFMing, I found that if the apex is on the board, one of the drill guides has a longer spigot to align the two holes
 

If your first cut is too short... Take the second cut from the longer end... LBD