If you've ever seen a construction crew tossing around tools, odds are high that you've also spotted a transit level in action. These optical instruments resemble telescopes securely installed on a tripod base, but they're more than just tools for looking up things or laying down lines. Surveyors and builders rely on them for establishing clear plumb lines, measuring distance and elevation, and determining the relative positions of objects.
The basic setup of a transit level consists of two spindles: one mounted inside the other, each attached to a circular plate, usually with a graduated horizontal circle and verniers to read angles in degrees or fractions. The upper spindle carries the telescope and locks it in place, while the lower one fits into a socket on the base and carries a calibrated rod that extends to about one hundred feet. The instrument is adjusted by leveling screws on the lower plate, clamps that hold the base in place, and tangent screws for setting up the telescope or circles in exact positions.
Unlike the simpler builder's level, the transit allows its user to shoot points of elevation and transfer them horizontally. For this reason, it requires the coordination of at least two individuals: one operating the telescope and the other manipulating the tape measure. Effective communication can be difficult given the cacophony typical of many construction sites. That's why it is prudent to equip yourself and your crew with communication devices like walkie-talkies.