Small theodolite tutorial or elementary surveying

Small theodolite tutorial or elementary surveyingQuestion:
One asks: Could anybody tell me the method using a theodolite to check if roll's are aligned 90 deg's to the external machine line datum. I've watched the surveyor's doing it and wondered how they worked it out. They use brass datum points in the floor, the offset machine datum line and check to rolls from these points. What's the method and math behind this? Is it all done by angles measured with the theodolite in surveying services?

First you have to set the theodolite on top the offset machine line. Then you check the point marked on the brass pads at both ends which were used to align the machine during installation.
The theodolite in land surveying jobs prefers to be the same height as the roll center and slightly away from the roll surface when looking along the roll. You turn 90 degree and put a ruler (with level) horizontally with one end touching the roll surface and pointing towards the roll center. Then you check the reading while the ruler is place at front and rear end of roll. You can have some different in reading indicates misalignment.

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