Craig Wasn't a Particularly Well-Grounded Individual

An engineer who likes to collect data everywhere he goes, Craig figured out how to mount a speedometer that uses a Hall-effect sensor on his 42-inch-long skateboard. By calibrating it for the 65-mm old-school wheels, he now knows his current speed, average and max speed (30 mph!), trip miles, and total miles traveled. Given the slight imbalance created by the wheel-mounted magnet, the only thing left for him to compute is a quick cure for road rash.