May seem a daft question, but how much discrepancy in levelling the bed is too much?
I'm aware it's bed twist that really matters, rather than end-to-end or exact side-to-side levelling, but how much twist?
I've found that my grandad's WW1 clinometer (used for setting up the sights on Vickers .303 machine guns - he was the final inspector in one of the factories!) is accurate to 1 minute of angle , which I think is an inch in about 95 yards, and can be set +/- 15 degrees consistently- accurate enough, too accurate?
Thanks all,
Dave H.