View Full Version : how to check if your level is level

01-13-2004, 12:24 PM
the thread on how surface plates were made years ago was very informative. i now have another question along that vein. i can see how a level could be checked for flatness, but how do you know that the level bulb is parallel to the faces of the level? how was the first level standard devised?

my guess is vertical can be found with a plumb line. then a surface 90 degrees perpendicular to plumb can be found to determine a horizontal line. how is this then transferred to a level?

andy b.

01-13-2004, 12:31 PM
It's not very often that something like a machine must be level. It must be true, not the same thing. Put the level on a flat surface and flip it end for end. If the level is adjustable then adjust until it reads the same both ways. If it isn't adjustable and doesn't read the same both ways consign it to use as a straightedge. It can be enlightening to check the run of the mill carpenters levels. I have a six footer that was cheap and is so far off that it's only use is for marking lines on plywood.

01-13-2004, 01:50 PM
I was thinking some more on your question. If you needed an absolute level calibration surface that was truly level in local gravity you could suspend a triangular (or square) surface plate on three EQUAL length wires from a single point and place the level on it.

01-13-2004, 01:55 PM
andy b.,

I'd guess that the first reference for 'level' was a still pool of water. With care this could be used as the 'master' against which a bubble level could be adjusted.


01-13-2004, 02:06 PM
as for determining if the vial is parallel with the base of the level... place the level on a flat surface and shim the indicated low end as neccessary to obtain a 'level' reading. Then flip the level, end for end, and replace it in the same footprint, with the other end now resting on the shims (if they were required in the first step). If you still get a 'level' reading, then the vial IS parallel with the base, and the level IS accurate. Assuming of course that the vial is rigidly fixed in its mounting and did not shift during the flip/flop.

01-13-2004, 02:33 PM
Have you heard of a water hose level? Set your level against that. Electronic levels use the concept of a pendulum attached to a flat surface.

01-13-2004, 02:38 PM
So, if you had a still pool of water and then freezed it... :-)

Just joking! Actually, that probably would not work for a variety of reasons.