Penalty on Exam: Minor
A calculator error is a pretty minor error as long as you show your work and your instructor can see what you tried to plug into your calculator. This is a big reason why most instructors want you to show your work (not the only reason, but a really good reason).
Remedy: Get to know your calculator. Ask your instructor to go over how to use your calculator properly. You could also watch my videos on how to use your calculator.