Originally Posted by
Metacortex
The design and drawing are what was intended to be produced while the actual production frames may vary, especially on hand made models. I normally assign frame angles by the design/build intention, since measuring 10 hand built frames down to the tenth of a degree will likely result in 10 slightly different results, especially if they are different sizes. I think there is way too much over-analysis going on here.
Using one physical example of a specific model to measure is also a problem, I'll see if I can measure at least 10 to maybe 20 Schwinn fillet-brazed frames to find the angles based off the top tube. That won't happen today though.
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.