On Jan 4, 7:09*pm, Josh wrote:
As for why I used the steel bars: *They were the straightest objects I
had on hand, plus they already had a lot slots & holes in them so I
could run a screw through them and into the studs easily.

Anyway, I did as many of you suggested and swapped the ends of the
level. *Sure enough, both bars are off 1/8" one way and dead level
when the level's ends are rotated. *Question is: which is correct?

I thought I could determine the "accurate" end by checking the bars'
level with a couple of 24" Craftsman levels I have. *One of shorter
levels showed the same thing the 48" level showed (dead on one way and
off 1/8" the other) and the other level showed a 1/8" error each, only
exact opposite depending on which way the level is orienated.

Guess I'll go with the longer level, and be careful to keep it
orientated the same way all the time. *Like someone above said, tile
rows don't have to be laser-precise level.

You need to check your levels and discard ones that are off
calibration. Find a rigid flat surface longer than the level. Place
the level on it, check the bubble and note the exact location
(centering is not necessary). Reverse the level (180 degrees). The
bubble should be in exactly the same location. If the level passes
this test it is OK to use it for your projects. If it fails, put it
on the curb and get a decent level such as Johnson or similar.
Considering the frustration you are having with your work, it would be
prudent to buy and use a laser level. Prices range from $20 to $400+
depending on what you want, but the cheapies from Harbor Freight are
perfectly accurate for tile work and the like.
Even a line level will do a good job. The level hangs from the center
of the line and needs two people to get it right. When anchored at one
end of the line, the other end is raised and kept fairly tight until
the bubble is perfectly centered. Framers and carpenters often use
these low cost tools for lengthy measurements. They are usually within
1/8" or so of a laser level line.

Joe

Joe