A tape measure gives us twenty-six numbers. They are the start, never the end. What matters as much is how you stand, how you sit and which shoulder you carry your bag on.
Most men have one shoulder lower than the other, usually the one they write with. We note it, and we cut the pattern to match. Nobody will ever see it; everybody will notice the jacket hangs straight.
We also watch the way you move. A man who drives all day needs a different back from a man who stands at a lectern.
Why it takes three fittings
A word on cloth weight