Finally, the Real Wheel

While you’re pondering the design of the Gear class, the future arrives. You show your calculator to your cyclist friend again and she tells you that it’s very nice but that while you’re writing calculators she would also like to have one for “bicycle wheel circumference.” She has a computer on her bike that calculates speed; this computer has to be configured with the bicycle’s wheel circumference to do its job.

This is the information you’ve been waiting for; it’s a new feature request that supplies the exact information you need to make the next design decision.