> Well, you measure it as it would be measured on a drawing, which is
> what it was made from. No need to over-think this.
> The only thing that isn't measured center-to-center is the seat tube
> length (when describing a frame) (sometimes).
> Think line drawings - where do the tubes' centerlines intersect, and
> where is the center line of things like the axles? Measure to those
Does the axle centerline define the length from the bb centerline on a long horizontal rear dropout? This is easier of course with a vertical dropout, but doesn't that 1" of wiggle room on a horizontal dropout confound being able to trust or assume absolute measures, even from a manufacturer?