Total Station Setup and Backsight Procedure

To set up a total station: (1) center over the control point with the optical plummet; (2) level with foot screws; (3) enter the instrument point coordinates; (4) aim at the backsight prism, enter backsight coordinates, and lock the circle orientation; (5) verify by shooting a third known point or checking the backsight distance. If the check shot fails, find and correct the error before doing any layout or as-built work.

Why Setup and Backsight Accuracy Is Everything

A total station measures angles and distances from a known point and orientation. Every coordinate it computes depends on: (1) accurate instrument point coordinates, (2) correct backsight orientation, and (3) proper leveling. Any error in these three elements produces a systematic offset in every subsequent shot — a 0.05-ft centering error shifts every stake by 0.05 ft. This is why the check shot matters.

Step-by-Step Setup Procedure

1. Set Up and Center Over the Point

Position the tripod over the control monument. Mount the instrument on the tribrach. Turn on the optical plummet or laser. Adjust the tripod legs until the plummet reticle is over the monument center. Level the circular bubble with the foot screws. Slide the instrument on the tribrach to fine-center, then re-level. Iterate 2–3 times until both centered and level simultaneously.

2. Precise Leveling

Use the electronic level display with the foot screws to fine-level. Rotate the instrument 180° and verify the electronic level reads near zero. If it shifted, split the difference with the foot screws and repeat.

3. Enter the Instrument Point

Enter the control point coordinates and elevation. This is the most error-prone step — verify a few digits against the control sheet before proceeding. A wrong instrument point shifts every shot by the distance between the correct and entered point.

4. Orient the Backsight

Aim at the backsight prism. Enter or select the backsight point coordinates. Press the orientation function — the instrument calculates the azimuth and orients the horizontal circle to your project coordinate system.

5. Verify with a Check Shot

Before starting layout or as-built work, shoot a third control point. The measured coordinates must match the known coordinates within the project accuracy requirement. If the check fails, find the error before proceeding.

Common Setup Errors

Prism Height

Measure the prism rod height to the nearest 0.01 ft and enter it in the instrument before taking the backsight. Wrong prism height produces an elevation error on every shot equal to the height error.

See also: Staking Out Building Corners and Foundation Layout and Traverse Closure and Adjustment.