Have you ever double-checked (in human fashion, not just using another calculator) the output from a calculator?

When calculators were first introduced I'm sure some people such as scientists and accountants did exactly that. Calculators were new, people likely had to be slowly convinced that these magic devices could be totally accurate.

But you and I were born well after the invention of calculators, our entire lives nobody has doubted that even a $2 calculator can immediately determine the square root of an 8-digit number and be totally accurate. So nobody verifies, and also, a lot of people can't do basic math.