All surveys begin with a reference point.
Any stream gager knows how cableways swing, sag, and sway, especially when the cablecar is attached to a lead weight swimming in flood water. Although the movement is tolerable for approximate depth measurements and average velocity, the movement biases readings from accurate sensors. The shore-mounted aluminum boom pivots in vertical and horizontal axes. Velocity meters and sonar transducers are mounted at the bottom of the vertical-support pipe. Relative elevation is determined by level sight to the staff plate on the boom.