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On Fri, 22 Aug 2008 21:41:50 -0600, pls  wrote:

> I think you are spot-or re the 30" levels. In the surveying world,
> level accuracy breaks down as follows:  A Wild T1 Theodolite, which
> was for many years the standard for low-order triangulation used a 30"
> bubble for leveling the instrument.  The next instrument up, a T2
> "Universal" theodolite had a 20" bubble -- it was so-called a
> "universal" because it could be used for every surveying application
> short of 1st and 2nd order triangulation, which required a Wild T3
> "Precision" theodolite, which had a 6.5" bubble.

One thing all three Wild models had was a "split bubble" lens and prism
set added to the level vial.  The bubble looked to be split in half
longitudinally, with the rear end half turned and flipped to be
bookmatched to the forward half.  Aligning the ends carefully with a fine
threaded screw would be much easier than reading two ends of the same
level vial between marks with a magnifying glass.  The advantage was that
the observer could be using a less sensitive bubble, which would settle
down more quickly, and have superior accuracy to the competition of the
time.

--
Richard . . .

Using Opera 9.2.4 after the "Dog" died

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