(a) On smooth or slippery surfaces, you should tighten the tripod's leg hinges while
setting it up to prevent the legs from spreading and causing the tripod to fall. If there are holes or cracks
in the ground, use them to brace the tripod. Sometimes, as a safety factor, you should tie the three legs
together or brace them with rocks or bushes after they are set to keep them from spreading. If setups are
to be made on a slippery finished floor, rubber shoes may be fitted to the metal shoes or an equilateral
triangle leg retainer may be used to prevent the legs from sliding.
(b) When you are setting up on sloping ground, place the third leg uphill and at a greater
distance from the mark. Set the other two legs as before, but before releasing them, make sure that the
weight of the instrument and the tripod head does not overbalance the tripod and cause it to slip or fall.
(c) Proper care must be observed in handling the tripod. When the legs are set in the
ground, apply pressure longitudinally. Pressure across the leg can crack the wooden pieces. The hinge
joint should be adjusted and not over tightened to the degree that it would cause strain on the joint or
strip or lock the metal threads. The tripod head should be kept covered with the head cover or protective
cap when not in use, and the head should not be scratched or burred by mishandling. When the tripod is
in use, the protective cap is to be placed in the instrument box to prevent it from being misplaced or
damaged. Any damage to the protective cap can be transferred to the tripod head. Mud, clay, or sand
adhering to the tripod must be removed, and the tripod should be wiped with a damp cloth and dried.
The metal parts should be coated with a light film of oil or wiped with an oily cloth. Foreign matter can
get into hinged joints or on smooth surfaces and cause wear. Stability is the tripod's greatest asset.
Instability, wear, or damaged bearing surfaces on the tripod can evolve into unexplainable errors in the
final surveying results.
b. Range Poles. A range pole is a wood, fiberglass, or metal pole, usually about 8 feet long and
about 1/2 to 1 inch in diameter. It has a steel-weighted point and is painted in alternate bands of red and
white to increase its visibility. The bands are 1 foot long and can be used as a rough measurement guide
using stadia estimation. Figure 5-12 shows a variety of range poles. The range pole is held vertically on
a point or plumbed over a point so that the point may be observed through an optical instrument It is
primarily used as a sighting rod for either linear or angular measurements. For work of ordinary
precision, chainmen may stay on line by observing a range pole.
Figure 5-12. Range poles
c. Plumb Bob, Cord, and Target. A plumb bob is a pointed, tapered brass or bronze weight that
is suspended from a cord to determine the plumb line from a point on the ground. Common weights for
EN0591
5-12
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