4. LEVELING THE THREE SCREW INSTRUMENT
Instruments utilizing three leveling screws are mounted on the tri-
pod and leveled in the following manner:
Mount the instrument on the tripod. Lock the telescope in place
with the lock lever and line up the telescope vial in position #1 as
shown (Fig. 2). Then grasp screws A & B so that both thumbs are
moving in opposite directions, either toward each other or away
from each other. Note that the bubble moves in the same direc-
tion as your left thumb. Do not permit the screws to come com-
pletely out of their bushings.
Keep about half the length
engaged. When the bubble
is centered in position #1,
turn the instrument and
observe the vial in position
#2. Now center the bubble in
position #2 using only screw
C.
Your David White Instrument
should now be leveled up,
but to be certain, double-
check. Rotate the instrument 180° so the vial is reversed. If the
bubble will not center when reversed, follow adjustment procedure
outlined under "Bubble Adjustments."
NOTE: Bubble adjustments must be correct if proper results are to
be obtained using the instrument.
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