On 11/05/2010 11:49 AM, Dave H. wrote:
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?
A master precision level is accurate to about .0001" per foot, not
exactly sure what that converts to in arc seconds. I use an electronic
level that is good to a couple arc seconds, and it is more sensitive
than I actually need.

Jon