An Old Surveying Staff
Called a Jacob's Staff
Early analog calculating devices were an outgrowth of the simple sighting devices used in both surveying and navigation. One of the simplest is the Jacob's Staff.
A Jacob's staff being used to find the altitude of the sun.
The crosspiece could be slid up and down the main part of the device until the sun was just visible over the top of the arm and the horizon under the lower portion. The altitude of the sun could then be found by examining the scale on the stick and noting where the arm cut the scale. This type of device usually had scales marked on them and this led to practitioners inventing more useful, and usually more complex, scales.
