It's a good point, but any numeric values used with a stepper control would be arbitrary. Apple's audio framework officially takes a value of 0-1 where 0 is muted and 1 is full volume, and then unofficially it takes a value of greater than 1 to go louder than full volume. So I could replace the slider with a stepper that moves in, let's say, increments of 5% where every 5% is a .05 change on that 0-1 scale. It wouldn't really be 5% louder, but it would be a frame of reference at least. Does that sound better?