Distinctive features of underground surveying are that stations are usually in
the roof instead of the floor; the object to be sighted and the crosshairs of
the telescope must be illuminated; distances are usually measured on the slope;
either the transit tripod has adjustable legs or a trivet is used; and often an
auxiliary telescope is attached to the transit, either at one end of the
horizontal axis or above the main telescope, with the line of sight of the
auxiliary telescope parallel to that of the main telescope. Horizontal and
vertical distances are computed from slope distances and vertical angles. The
transit is set up at one station, being centered by plumb, and the vertical
distance from the station to the horizontal axis of the transit is measured. A
plumb bob is hung at the next station, with a point on the plumbline marked by
some form of clamping target. The vertical angle to the point so marked is
measured, and the distance from horizontal axis to the target is taped. Urquhart
Source:
Dictionary of Mining, Mineral, and Related Terms
