Positioning front mech on seat tube

pollys_bott Posts: 1,012
edited November 2013 in Workshop
OK, so when you get a new front mech it has that nifty bit of plastic with the teeth outline showing you exactly where to position it on the seat tube. What about when you're moving components across to a new frame - any clever tricks to get the mech in the right place first time or is it down to an educated guess then jiffle up / down as necessary? From memory I'm guessing that the top of the chainring teeth want to be 2/3mm below the top of the mech cage when the chain is on the big ring, yes?