In article , "CWLee" wrote:

I inherited (from a building contractor buddy) a small
tool/device. I can't post a photo here, but the visually
imaginative readers can picture what I mean from the
following description.

There are numerous sites where you can post photos, free of charge. Try flickr
or photobucket -- or if you have a Facebook or Myspace page, you can post
there too.

It is cylindrically shaped, about 1.5" diameter, 6" long, in
a metal case. Lens at each end. Acts as a low-power
telescope. The top of the device has a bubble level, with
optics such that when standing on one side of a room, and
looking across it, one can not only see the other side of
the room but also the bubble level and a horizontal marker.
One can raise and lower the angle of the device so as to get
the bubble in the center of the markings, and that allows
the user to see, on the far wall, what is exactly at eye
level.

Sounds like you're describing a surveyor's level of some sort. You might find
this interesting:
http://www.surveyhistory.org/the_sur...asic_tools.htm

I don't know what building or other application would call
for such information, but that appears to me to be what the
device is designed for.

My question is: What is this called in the trade? In what
trade would that be? Surveying? Plumbing?

Surveying, clearly.