[stavros]

Well if you haven't seen enough calculators to see one that can't add, a very common issue with floating point arithmetic on computers, you shouldn't offer your experience as an argument for anything other than that you haven't seen enough calculators.

[wat10000]

How many calculators do I need to have seen in order to make the claim that there are many calculators which are essentially 100% reliable?

Note that I am referring to actual physical calculators, not calculator apps on computers.

[stavros]

Well, to make the claim you actually made, which is that you haven't seen a single calculator that was wrong, anywhere from zero to all of them. It's just that the "zero" end of that spectrum doesn't really tell us anything about calculators.

[wat10000]

When was the last time you saw an actual calculator (not an app) give a wrong (not merely rounded) answer?