This one is for the math geeks. One of the most annoying mistakes for me is when I try to solve one line of algebra and get 6 different answers on my calculator after trying to solve it 14 times, and still and up with the wrong answer. That makes me want to tear about the sheet of paper with my work on it, and destroy my calculator. (I still use my TI-89 from time to time...though 3/4 of my Casio's broke on me after taking maybe 10% of the damage my TI-89 has received. Still, the TI-89 has all working buttons, etc.) Damn those multiple wrong answers, oh, and the cause of the wrong answers was from writing a 1 for a 2. So annoying.