Callibration problem

I have completed callibrating my accelerometer of apm version 2.8…In this,Altitudes are nearly zero.(balanced)… but a few day later, it changes into a value showing that the apm is not in balanced position… Do i need to redo accelerometer Callibration? …I have repeated it again and again…

Did you saved everything you edited ?
May there be a Problem with your Accelerometer ?
How old is your setup ? (Hardware)

Sometimes a hard bump can mess up the calibration, but if you have done the calibration and a few days later it is bad, how bad is it? a few degrees, or about 10 degrees or more off?.

But if its over 10 degrees and you have not had any crash, then it is likely that the accelerometer is faulty on your APM.