Summary: I have had this model of calculator since the 1980's and still my favorite financial calculator. The thing needs batteries every five years even with daily use. I have three of this model of calculator with one in my briefcase and two in my office. Great product and is well worth the price.
Summary: Sticky keys! To Temporarily fix it Reset the device by powering on while holding the minus sign. Make sure to hold the minus key for at least 10 seconds after releasing the ON button or else the sticky key syndrome returns. I wish I realized the sticky key problem sooner so I could have returned it during the one year warranty period. I also that wish they still made the scientific version that let's you delete one digit at a time instead of clearing x entirely.
Summary: This is my third HP 12C calculator. Both of the predecessors had problems with the display going black after 15 years or so. I completely love the unit and think that RPN calculators are the way to go. I expect to get 15 years out of this one too.