Procedure to "Buck-In" a Theodolite or Transit
If you need to square a roll on a machine, or transfer a point from the line to an overhead conveyor, an instrument needs to be "bucked in".
What this means is to locate the instrument exactly on a line parallel to, say an offset centerline, or to a location between two other known points of reference.
Repeatable results require careful and thoughtful actions by the instrument man. Care must be taken to protect the instrument AND the reference points.
First, select the point to set up the instrument on a tripod. This point should be between two reference points. The tripod should be in good condition, preferably made of wood and the use of a tripod stabilizer is recommended.
Set the tripod at a suitable height and be sure to use a torpedo level to level the top of the tripod. It is very important to have the top of the tripod LEVEL.
Mount the instrument and locate point A carefully with the vertical reticule, and lock the instrument so it cannot rotate. Plunge the telescope and observe point B. Move the instrument to the left or right until point B is in line with the vertical reticule.
Plunge the telescope and locate point A. Now unlock the instrument and rotate the instrument until point A is in line with the vertical reticule and lock the instrument.
Repeat this procedure until the instrument is "Bucked In", always rotating at point A and moving left or right at point B. A lateral slide is a wise choice to move left or right if available.