Page 55 - Moving the Earth_ The Workbook of Excavation

SURVEYS AND MEASUREMENTS

SURVEYS AND MEASUREMENTS 2.5

FIGURE 2.5 Magnetic declination map. (Courtesy of U.S. Coast and Geodetic Survey.)

FIGURE 2.6A Leveling screw action. (Courtesy of David White, LLC.)

If both screws are turned to the left (clockwise), or one is turned left while the other is sta-
tionary, they will be jammed; while if one or both are turned to the right (counterclockwise), they
will both lose contact.
The screws should be kept in light contact with the plate during the adjustment and tightened
somewhat as it is finished.
When the bubble is approximately centered, the telescope should be swung 90 degrees so as to
be over the other pair of screws, which are used to center the bubble in the same manner. This
adjustment will disturb the first one, so the telescope must be swung into its original position and
leveled, this time more exactly. It should then be checked in the second position, and adjustment
in the two positions made alternately until it does not move during the swing through this quarter-
circle arc.