Calculators in general were pretty damned well made in the 1970s/1980s because they were relatively expensive. Or actually expensive, in the 1970s at least. I "collect" (read pile in the closet) old calculators and about 90% of the ones I find work just fine after decades of sitting around. I prefer the LED models from the 70s (esp the blue ones) but have probably three dozen <1990 calculators and they all work great with fresh batteries. Including the programmable Sharp model I bought originally in 1983.

Not so sure many calcs purchased new today would still be working in 30+ years.