Just Wondering wrote:
On 12/30/2017 3:15 PM, Emanuel Berg wrote:
Just Wondering wrote:

What is the theory behind levels? I've heard
that carpenter's are more precise than those
used by bricklayers. I have examined the
ones we have here and there is no indication
as to precision on either so the only way to
tell would be the mortar stains on one of
them...

Use it to "level" a board, then put a cup
filled with water on the board. The cup will
confirm whether the board is level.

Isn't that to take it back a level, having to
use utensils to verify your tools?

Perhaps. I was responding to the stated example about
"the only way to tell" with another way to tell. As
someone else pointed out, you could also check with
your level oriented in one direction, then turn your
level end-for-end and compare the result. There are
probably lots of other ways to tell.

After about 25 posts, no one has come back to the OP's point that a
level can indicate that a surface is level ("both ways") even for a
surface which is slightly off-level. Different levels have different
tolerances by design. As I indicated in my post, a 100% accurate level
would be a PITA. But, I believe that there are different categories of
bubble levels. I think this is left to be addressed.