Egypt

I have known that the pharoahs had a gauge near the 1st cataract to measure the height of the Nile, especially during the annual flood. I had understood this to be a means of knowing whether the flood would be in the optimal range for good crops, too low meaning drought and bad harvests, or too high with destructive floods. It turns out this is only partly true. They were also used to determine taxes, and every city had its own nilometer to gauge the flood in that specific location to accurately determine taxes based on local conditions rather than a generalized single reading. Apparently local conditions varied enough to make this locally important.
The 1st picture is of the one I knew about, one of the 2 at the Philae Temple (see another post) near Aswan below the 1st cataract. The others are at Kom Ombo, Edfu and Hatshepsut's temple on the west side of the Nile at Luxor, respectively. These are all located at temples (see other posts).
I note that the nilometer for Luxor (east bank) would likely be at Old Luxor. As that location has only recently been discovered, excavation is ongoing and not open to visit.
In case you're wondering, one of my responsibilities in a "previous life" involved work in both surface and groundwater hydrology. Hence my interest in 4,000 year old approaches to the scienceEn savoir plus