The staff is linear scale which must bee held vertically (it includes a spherical level) on the point involved in the height difference to be measured. The precision of its graduation and its maintenance in a vertical position strongly influence the precision of the height difference measured.
A level's reticule is usually made up of four wires:
₪ The upper stadia wire
₪ The lower stadia line
₪ The leveling wire
₪ The vertical thread
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