Originally Posted by
repechage
Earlier you acknowledged, my paraphrasing that a top tube could be .7 degrees off, I agree, no problem, except if that is your Datum then the head angle will be off an equal amount and the trail measure will be off too. That could well be significant if you wanted to compare different brand bikes and or wanted to replicate a bike you have and liked.
I said that "a combination of tolerance stack, geometry variations due to frame size differences (geometry varies slightly in sizes other than on the official drawing) and finally measurement accuracy all contributed to your 0.7° measurement.", referencing Scoopers top tube being 0.7 degrees off horizontal, despite that the factory drawing showed that it was designed to be horizontal. Add in variations in the fork and headset and you have even more reasons to come up with that discrepancy.