You don't need to transform degrees and radians. You have a relative value:
CGFloat relativeAngle = [_Weight.text intValue] / 300.0;
So just use it:
_Arrow.layer.transform = CATransform3DMakeRotation(relativeAngle * M_PI*2, 0, 0, 1);
If the start is wrong just change the initial position of your view.
(Or sum up the wrong angle to the new angle. Like (relativeAngle * M_Pi*2 + correction)
.
// what PI means in degrees
M_PI * 2 = 360°
M_PI = 180°
M_PI_2 = 90°
M_PI_4 = 45°