How do you tell if a level is accurate?

snipped-for-privacy@none.com posted for all of us...

DAGS

John G posted for all of us...

Ashton Crusher wrote in news: snipped-for-privacy@4ax.com:

If it reads differently end for end on *any* surface, level or not, it is out of adjustment.

If it reads the same end for end on *any* surface, level or not, it is properly adjusted.

That simply is not true; see above. If the bubble centers, and remains centered when the level is reversed end for end, you know two things: the surface is level, and the level is accurate. If the bubble does not center, and remains off center by the same distance in the same direction when the level is reversed end for end, you know two things: the level is accurate, and the surface is not level. If the bubble does not center, and remains off center by a different amount and/or in the opposite direction, you still know one thing: the level is not accurate.

First thing you've stated correctly -- and you apparently didn't notice that it contradicts everything else you wrote.

It was said up thread a couple of times but never in such clear terms.