When I went to England in ’75 to learn how to build frames, I used my Italian Masi Gran Criterium I had gotten in Milan in ’72 as a geometry pattern to build my own frame. I very carefully measured the seat/top tube angle with a vernier protractor. It read 73º30” so I made my new frame the same angle. Except later I discovered that the seat tube’s real angle was just 73º to the ground because the top tube was tilted. My discovery got several Masi owners on the Classic Rendezvous list to measure their frames and everyone’s top tube was not level by 6 to 9mm.