Whit, when i said i take a "good guess" i was referring to a new design that's never been flown before. if you're building from plans you don't have to guess at anything, the designer has already worked everything out. the only thing you might have to guess at is what constitutes "level" when hanging the plane in the sling and that's most likely going to be the same attitude as shown on the plans....and as someone else pointed out, eyeballing it is going to get you closer than you need....even if you have a few grand in the model.

there is no such thing as a "correct" flight attitude either...unless you also know the exact speed, weight, elevation, etc., etc.