First of all, I tell you how you should have changed the batteries in case you have not done it yet, to make you know by the next time. That problem is very common and easy to solve. Message: I cannot make the calculator work after changing the batteries, the TM, SN error codes appear, and nothing works.
I got an email of someone whoes calculator Casio 880 is having troubles after changing the batteries, as it is a very common failure on Casio FX-880P and FX-850P, I write here the question and the solution.
