NSNumberFormatter different on device and simulator

I have a UITextField, using this code, print the value on the label at the bottom and formatting it.

NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
[formatter setNumberStyle:NSNumberFormatterDecimalStyle];
[formatter setUsesGroupingSeparator:NO];
[formatter setMaximumFractionDigits:2];
[formatter setMinimumFractionDigits:2];
NSNumber *calcolo = [NSNumber numberWithDouble:[value1 doubleValue]-[self.textfield.text doubleValue]];
formattedString = [formatter stringFromNumber:calcolo];
self.label.text = formattedString;

On the simulator (U.S.), the value is displayed correctly. On the device (IT), there is the comma on keyboard, but the value after the comma is always zero.

EDIT: This works

NSNumber *temporaryValue1 = [formatter numberFromString:[NSString stringWithFormat:@"%@",value1]];
NSNumber *temporaryTextField = [formatter numberFromString:self.textField.text];
NSNumber *calcolo = [NSNumber numberWithFloat:([temporaryValue1 floatValue] - [temporaryTextField floatValue])];
formattedString = [formatter stringFromNumber:calcolo];

I don't think the issue is your output. The issue is the input you get from -[NSString doubleValue]. That method doesn't honor the user's locale.

You should be able to use the formatter you made to convert self.textField.text to a number properly respecting the locale. Or you might consider using NSDecimalNumbers, especially if this is currency (looks like it?). Then NSDecimalNumber has a method +decimalNumberWithString which also does the right thing for you.