VBA function doesn't work properly

I can't understand why my rate1() function (my macro) doesn't work properly. While I'm dragging M5 cell in Sheet2 down to M14 cell it gives the wrong result. Even when I change value in Sheet1 and refresh data of pivot table in Sheet2, my function rate1() isn't updated. But my problem is solving (getting the correct result) when I'm going Edit Mode (pressing function key F2) in active Cell M5 or M6 or M7..so on and pressing Enter each time.

Is there any explanation?