Just remember, inclinometers that work using a weighted pointer are only accurate if the bike is on perfectly flat ground and is perfectly upright. Protractors that measure the angle between top tube and seat tube can be used in any orientation, but the reading does not reflect the effective seat tube angle if the top tube is not built as horizontal, or if the tube tapers in some way. This is obviously a problem with off-topic frames, but even classics can have non-horizontal top tubes. If your front and rear tires are different profiles, or you lower headset parts have an unusual stack height, the TT will slope when the bike is on flat ground. Replacement forks can also jack up the front or rear of teh bike.
FWIW, I level the bike on a windtrainer using a 4' carpenters level over the axles (assumes I use matching ft and rr tires) and then measure the seat tube with a cheapie Craftsman dangle-thingy. Good to the nearest .5 degrees by my reckoning, which ain't so great. On my size bike (78.5 cm frm BB center to top of saddle) that's over 6mm of offset.
Tom Dalton
Bethlehem, PA
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