@Adam Behringer , it is much more better to use this code for getting RoundMode correct !!
result=[[self math] calculations];
resultString=[NSString stringWithFormat:@"%.16f", result];
getIntPartOfValue=result;
stringForGetIntPartOfValue=[NSString stringWithFormat:@"%lld",getIntPartOfValue];
[numberFormatter setMaximumFractionDigits:(maximumAmountOfDigits stringForGetIntPartOfValue.length)+1];