Figure 20. Horizontal, vertical, and collimation slow-motion screws, adjustment.
and sand are allowed to remain on threaded or sliding
internal stresses and distortion in the instrument and
surfaces, moving parts of the theodolite will soon bind
produce poor sightings due to heat waves. If possible,
and the instrument will become inaccurate or
the theodolite and the instrumentman should be
inoperable. The theodolite should be brushed frequently
protected from the direct sunlight by an umbrella or
and carefully wiped clean. Be extremely careful not to
other suitable means. Under these conditions, shorter
scratch lens and prism surfaces during cleaning
sightings will decrease the amount of sighting errors.
operations. Always protect the instrument from blowing
Taking sightings during early morning and late evening
dust and sand. Place a protective cover over the
will also minimize error magnitude. The use of suitable
theodolite when it is not in use.
dark glasses by the instrumentman will reduce eyestrain
and fatigue. If the theodolite is kept in a cool storage
place, it should be removed from storage in sufficient
21. Operation Under Rainy or Humid Conditions
time before use to allow the metal temperature to
In humid areas, a slight lowering of the temperature will
approach that of the outside air.
cause condensation of moisture and fogging of lenses
20. Operation in Dusty or Sandy Areas
and prisms. Internal fogging can usually be removed by
placing the theodolite in a warm, dry place. Corrosion
Special care must be given instruments which are being
caused by high humidity can be partially eliminated by
used in dusty or sandy areas since both dust and sand
using warm, dry storage
are highly abrasive. If dust
AGO 5078A 27
