a. Unpacking and Performing Instrument Setup.
(1) Erect the tripod over the station point, hang the plumb line by the hook on the central fixing
screw, and center the tripod to 1 or 2 centimeters. For instrument stability, tread the feet of the tripod
firmly into the ground. For precise measurements, see that both the tripod and the instrument are
completely protected from the direct rays of the sun.
(2) Grasp the two ends of the leather strap of the instrument casing, and draw them forcibly
outward so that the two lever fastenings open and the hood can be cautiously lifted and removed.
(3) Loosen the three black screws that hold the instrument to the bedplate of the casing and draw
back the three slides. Lift the instrument using its two scope supports, and place it on the tripod in such
a way that the illuminating mirror for the horizontal circle (9) can be turned toward the light. Screw the
central fixing screw of the tripod into the footplate of the instrument and, after centering the instrument
exactly over the point with the plumb line, tighten the fixing screw.
(4) To set up the instrument on an observation pillar, set the cast-iron base plate on the pillar and
accurately center it using a centering pin with a circular level. Place the instrument on the base plate and
affix it by turning the central fixing screw with the provided pin.
b. Instrument Leveling. Turn the upper part of the instrument into such a position that the plate
spirit level (15) between the telescope supports lies parallel to a line joining two of the foot screws (20).
Turn the two foot screws simultaneously but in opposite directions until the bubble in the level is
centered. (The bubble sensitivity of the plate level is 5 to 7 seconds per 2-millimeter graduation.) Turn
the upper part of the instrument through 90, and again center the bubble by turning the third foot screw.
Turn the instrument through 180,. If the plate spirit level is correctly adjusted, the bubble will come to
rest at the center. If the bubble is off center, move the bubble halfway back toward the center using the
plate-level adjusting screw. Center the bubble in its vial by turning the foot screws. The resulting
position of the bubble is called the adjustment position. It corresponds to a vertical position of the
vertical axis. Repeat this test, making any additional required adjustments of the plate spirit level. The
adjustment of the plate spirit level should be tested every time the theodolite is set up for use. It is
essential that the plate spirit level be protected from the direct rays of the sun; otherwise, the position of
the bubble will not remain stationary throughout a complete rotation.
c. Focusing. Direct the telescope toward the sky or a light source. Without observing the
background, turn the edged, black diopter ring on the telescope eyepiece (6) until the crosshairs appear
sharp and black. Note the setting on the numbered scale. This will remain constant for one observer.
To focus to obtain a clear image of a sighted object, turn the focusing ring for the telescope (3). Test
your absence of parallax between the crosshairs and the image by moving your eye
3-17
EN0593
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