right standard (opposite the vertical circle) while you are attaching it. The automatic and dumpy levels
should be held at the center of the telescope. Both theodolites and levels should be gripped near the base
of the instrument with the opposite hand. The instrument should be screwed down to a firm bearing but
not so tightly that it will bind or the screw threads will strip.
Figure 5-9. Tripod detail
(1) Types. There are two types of tripods that surveyors use: the fixed leg and the extension
leg (see Figure 5-10). These tripods can also have wide frames like those shown in Figure 5-11, which
have greater torsional stability and tend to vibrate less in the wind.
(a) Fixed Leg. The fixed-leg tripod is also called a stilt-leg or rigid tripod. Each fixed
leg may consist of two lengths of wood as a unit or a single length of wood split at the top, which is
attached to a hinged tripod head fitting and to a metal shoe. At points along the length of the leg,
perpendicular brace pieces are sometimes added to give greater stability. The fixed legs must be swung
in or out in varying amounts to level the head. Instrument height is not easily controlled, and the
observer must learn the correct spread of the legs to get the desired height.
(b) Extension Leg. The extension-leg tripod is also called a jack-leg tripod. Each
extension leg is made of two sections that slide longitudinally. On rough ground, the legs are adjusted to
different lengths to establish a horizontal tripod head or to set the instrument at the most comfortable
EN0591
5-10
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