Great reliable calculator. Bought mine in 2001. A couple buttons stopped working within in 6 months. I sent it back to TI and they promptly replaced it with the one I have now. After all this time I figured I should replace the working battery as a preventive measure. (IT would be bad to have the battery suddenly go dead in the middle of an exam). Some professors won't allow allow a "grapher" on their exams, such as my Calc II professor. This calculator has always been an approved alternate to a my TI89.