Wes wrote in news:1177032145.364625.286810
@d57g2000hsg.googlegroups.com:

"The 6" through 18" (150-450 mm) main level vials have graduations
that are approximately 80-90 seconds or .005" per foot (0.42 mm per
meter). There are five, six, or seven lines on each side of the
bubble, depending on the base length.

Wes, I agree, that is entirely practical. As far as bubble technology goes,
senstivity easily exceeds that, IIRC the plate bubble sensitivity on
theodolites is commonly around 20" (seconds) per 2mm run. By reversing such
a bubble and splitting the difference, it should be possible to achieve an
error well under 0.1mm/m slope.

Realistically, most bubbles for engineering workshop use would be more
accurate than the drilling process, so they are a quite adequate means of
registering the work.

I have used them with success, but prefer an indicator that I can see
clearly while tightening the vice.

Owen