On Sun, 31 Dec 2017 01:29:43 -0500, Bill
wrote:

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.


I've addressed it.
There ARE different "sensitivities" of level - call it "accuracy" if
youi like - or "resolution".

It is specified by number of degrees per unit of measurement bubble
displacement - such as .05/2mm, or in units per unit of deflection -
like .2/1 - 0.2 inch bubble deflection with one end of 3 meter
level raised 1 inch.

Can also be metric.
An engineer's precision level (machinist's level) or a survey transit
may be as accurate as .005 degree per 2mm bubble deflection, while a
carpenter's square is tiypically closer to 1 degree - and a plumber's
level may have 3 or 4 vials of different accuracy for measuring
different "drops" for different drain or pipe installations

As far as a level being able to measure totally level both ways on a
surface that is not level - not possible. Even the cheapest level will
only read level on a level surface, both ways, if it is level to
within a VERY small limit of error - if you can read the bubble
accurately