Dealing with operator error is different from having doubts about the accuracy of an appliance. For quite a lot of things done on a calculator, trying to judge

Dealing with operator error is different from having doubts about the accuracy of an appliance. For quite a lot of things done on a calculator, trying to judge whether the numbers seem 'right' is going to be difficult. A more reasonable way to reduce operator error is to key the calculation through the device a couple of times and make sure you get the same answer.