I have been reading about the desired for a 3-position preselect and have an observation.  Mine has an infinitely-variable mechanical preselect system and I find that I use about 4 positions, not 3.  One is for takeoff, one for "normal" landing and the 4th for "high drag."  I usually select 10 degrees on downwind, and then on base or final add more.  I then adjust power to make the landing.  If I have the power completely off and I'm still high I will go to full flap deflection for extra drag.  So to me there are 4 useful positions - up, 1/3(takeoff), 2/3(normal landing) and full(max drag).  There might even be more - on a hot, heavy and high takeoff I'll retract takeoff flaps in two or three small increments.  I thought about making an electric system, but the brain strain was too great and I went back to a mechanical system - one cam, 4 microswitches and no relays.

Gary