Warning: a guy at the co-op in Ann Arbor taught me to tension spokes by ear, and I still think about him
Back in 2011 I was working at a shop and a walk-in customer named Ray asked me to true his rear wheel. I started squeezing with a tensiometer when he put his hand up and said, "Stop, just flick the spokes and listen." He pulled a folded piece of paper from his wallet, a chart he had drawn in 1974, and tapped each spoke with a screwdriver handle. He showed me that a wheel sounds like a low note when it is loose and a high ping when it is right. I still keep a copy of that chart taped inside my tool chest. How many of you still true by ear, or is everyone on gauges now?