in my calculator ,while i type or click digit like 3 to 4 numbers the screen refresh automically ....i mean when i click my fourth or seventh number the screen auto refresh and all type on screen are being deleted...on the other hand sometimes screen not shown to me...if i click a digit for a while the screen shown to me then i press of the digit screen are off....i changed my battery...now what should i do? is this repairable?