Equipment used contained by building and measure erosion/gradient of ground?

A while ago I had a field trip next to my geography class at a beach and we used this thing that looked close to a camera to measure the erosion on this path and i can't remember what it be called. It had three legs and i swear it be called a tri-something. I think the conception of it was that it stayed at the same rank and could measure the drop in altitude without moving or something.
Help me out please?!?! What was it call and what exactly does it do?!
Answers:
That is a surveying instrument. It is either a transit, engineer's level, dumpy plane or theodolite. These four equipments are used to measure and determine the ground levels/elevations, slopes or gradients, distances, angles, bearing or azimuths. They are all mounted on a three-legged object call "tripod".

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