They are accurate enough to be useful, unless you get a dud.jb wrote: ↑27 Jun 2022, 10:42pm Why anyone would expect the park tool or any similar make to be particularly accurate is a bit of a mystery, I expect mine to be reasonably consistent but you are best trying it on known good wheels to get a feeling of where the right tension lies. If I remove the spring from mine the nylon pointer bit binds slightly in the slot so that's going to throw it out for a start. Oiling it will also affect the reading.
Otherwise, how was your "known good" wheel built? Or perhaps it came down from the mountain with Moses and the commandments?
The OP (Mr Tom) put his gauge on a known good wheel from a known builder, and the gauge gave insane readings....ie his gauge is a dud.
When I was building wheels at Spa I built some in the shop using one of the shop gauges, and some at home using my gauge. You couldn't tell the difference. I don't think we ever had less than 3 people building wheels in the shop or at home, and we all built to the same tension, using our own gauges at home and one of the shop gauges in the shop.