Gradient - An alternative to measuring vertical angles in degrees, the gradient is
defined as the tangent of the vertical angle with respect to the horizontal times 100%.
For example, a gradient of -50% means a slope of 22.50 below the horizontal.
Face left - The theodolite position in which the vertical circle is on the viewer's left
while he looks into the telescope.
Face right - The theodolite position in which the vertical circle is on the viewer's right
while he looks into the telescope.
Horizontal circle - The graduated circle in the horizontal plane that the theodolite
reads out to measure horizontal angles.
Horizontal clamp - Thumbscrew that can be used to fix the angle of the theodolite
with respect to the vertical axis. When the horizontal clamp is tight, the instrument
can be translated horizontally with the slow-motion screw.
Line of collimation - The line of sight through the centre of the telescope crosshairs.
Optical plummet - Small telescope whose eyepiece is near the bottom of the
theodolite that looks at the directly beneath the theodolite and is used for centering.
Round of angles - A complete set of angle measurements performed first in the faceleft,
then in the face-right position.
Slow-motion screw - The fine adjustment screw used to translate the theodolite in the
horizontal or vertical plane when the horizontal or vertical clamp is tightened.
Trunnion axis - The axis about which the telescope pivots.
Vertical axis - The axis about which the horizontal circle pivots.
Vertical circle - The graduated circle in the vertical plane that the theodolite reads out
to measure vertical angles.
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