Originally Posted by
repechage
Having two reference datums is an engineering and production no-no. I will go with the one that matters, the axle centerline datum.
We don't know which datum they used, which is why it would be great to hear from Waterford. If I were designing a frame I would want to base the main triangle off of a directly connected (i.e. welded or brazed) part, meaning either the top tube, seat tube or head tube.