with a 3-piont setup, i meant that the switches always rest on 3 sets of contacts.. just like my probe, and about any other one.. the "one switch" probe that's also posted in this thread doesn't have that setup, so it will be very hard, if not impossible to set it up right.. and have it fuctioning well..
recently i've designed a probe that's both easy to build, and accurate, it uses a disc-shaped piece of PCB, 6 copper or brass studs, and 3 steel bearing needles( or similar material, like shafts of drills )
http://i12.photobucket.com/albums/a2...e-1/probe3.jpg