29.242
Figure 11-7.-An engineer’s transit, exploded view.
center of a circular plate and accurately fitted the
socket in the leveling head. The lower plate contains
the graduated horizontal circle on which the values of
horizontal angles are read with the aid of two
verniers, A and B, set on the opposite sides of the
circle. A clamp controls the rotation of the lower plate
and provides a means for locking it in place. A slow-
motion tangent screw is used to rotate the lower plate
a small amount to relative to the leveling head. The
rotation accomplished by the use of the lower clamp
and tangent screw is known as the LOWER
MOTION.
Upper Plate or Alidade Assembly
The upper plate, alidade, or vernier assembly
consists of a spindle attached plate to a
11-15
