This simple circular slide rule works the way your aviator watch does. For rate/time calculations it can be faster than a calculator: set the rate once and read every distance and time straight off the dial, without typing anything. If you're an aviator who would rather use a slide rule than a calculator, try this app. It is much easier than trying to punch numbers on a watch calculator. We created it for the watch, but it works on the iPhone and iPad, too. Rotate the outer ring with your…