Language Hat has an interesting post on the etymology of ‘theodolite’, which he treats as some kind of exotic or obsolete scientific instrument. I have used one on the job, though not in the last quarter-century. From 1978 to 1982 I worked for a company that measured air pollution from moving trucks and airplanes, a process my boss invented, and we used theodolites to measure the winds at various altitudes. They were not carried along on the trucks and planes, but set up on the ground to track pink gas-filled balloons. As I recall, a theodolite is just a device to measure the precise direction in three-dimensional space from one’s own location to any object within sight. For instance, it may show that a neighboring hilltop or mountain peak is located at a bearing of 343°, i.e. north by northwest, and 12° above horizontal. It’s basically a small telescope on a tripod, with a plumb bob to level the platform, a compass to line it up north and south, and horizontal and vertical cranks with numbered dials to aim the sight and measure the vertical angle above (or slightly below) the plane of the earth’s surface and the horizontal angle clockwise from due north. One worker would turn the two cranks to keep the balloon in sight of the little telescope as long as she could, while another recorded the azimuth and elevation at set intervals of time. Our primitive computers (7K RAM, 40-character LED display, audio-casette storage — a bargain at $15,000 each) would then calculate the wind direction and (I think) speed at various heights, or perhaps we did that part on graph paper — it’s been a long time. As I recall, plumes emitted from power plants tended to skew clockwise as they went up, and sometimes had more complex shapes. We needed to know where the winds were blowing to decide where to send the truck or airplane.
As for the etymology, I told my fellow-workers at the time (an overeducated bunch) that ‘theo-dol-ite’ should mean ‘an instrument to fool the gods’. We looked it up, and Webster’s or Funk and Wagnall’s or whoever it was said that it means ‘an instrument for seeing clearly’. If so, the inventor messed up two of the vowels, since that should be a ‘theadelite’.