I spent two weeks in a basement workshop outside Zurich, learning to draft by hand. Not because I needed to — CAD replaced the drafting table decades before I was born — but because a retired mechanical engineer named Hans refused to teach tolerancing on a screen. "You must feel the weight of the pencil," he said, guiding a 0.3mm clutch pencil across a sheet of vellum. He was right. The graphite taught me something no parametric model ever could.
The Tolerance Stack
Every dimension on an engineering drawing is a contract, not a measurement. When Hans marked a bore at 25.000 mm, he was defining an acceptable range — not stating an absolute truth. The ISO system of fits translates this into compact notation: H7/g6 for a sliding fit, H7/p6 for interference. Five characters that compress decades of manufacturing practice into something a machinist in Osaka and an engineer in Stuttgart can both read without ambiguity.