If ever there was a site that lovingly and obsessively detailed the history of a narrow slice of technology, it is the Museum of HP Calculators.
I can’t blame them. I still remember the reverent awe of using the HP-35 at the calculator counter at Macy’s as a school kid. During high-school I somehow bought (or was given?) an HP-41C. It had the form factor of a calculator, but had a one-line alphanumeric display, and was programmable with a rudimentary assembler-like language. I wrote a few interesting programs for it (generate pronounceable nonsense strings, test whether the axes of the three inscribed parabolas of a triangle are coincident), all of which are lost in the sands of time. I still have the calculator, and it might work if I found some batteries for it.
The museum is an amazing site, with history not only of every HP calculator, including pictures, technical specs, and manuals, but also earlier calculators and slide rules.