are used to center, as much as possible, the bubble of
the bulls-eye level. The line of sight automatically
becomes horizontal and remains horizontal as long as
the bubble remains approximately centered.
The hand level, like all surveying levels, is an
instrument that combines a level vial and a sighting
device. Figure 5-4 shows the Locke level, a type of
hand level. A horizontal line, called an index line, is
provided in the sight tube as a reference line. The
level vial is mounted atop a slot in the sighting tube
in which a reflector is set at a 45° angle. This permits
the observer, who is sighting through the tube, to see
the object, the position of the level bubble in the vial,
and the index line at the same time.
To get the correct sighting through the tube, you
should stand straight, using the height of your eye (if
known) above the ground to find the target. When
your eye height is not known, you can find it by
sighting the rod at eye height in front of your body.
Since the distances over which you sight a hand level
are rather short, no magnification is provided in the
Figure 5-4.Locke level.
SETTING UP A LEVEL
After you select the proper location for the level,
your first step is to set up the tripod. This is done by
spreading two of the legs a convenient distance apart
and then bringing the third leg to a position that will
bring the protector cap (which covers the tripod head
threads) about level when the tripod stands on all
three legs. Then, unscrew the protector cap, which
exposes the threaded head, and place it in the
carrying case where it will not get lost or dirty. The
tripod protective cap should be in place when the
tripod is not being used.
Lift the instrument out of the carrying case by
the footplate-not by the telescope. Set it squarely and
gently on the tripod head threads and engage the
head nut threads under the footplate by rotating the
footplate clockwise. If the threads will not engage
Figure 5-3.Self-leveling level.