A knight may move exactly 1+ square root of 2 squares in any direction that lands it exactly in the center of another square.
Try not to think about that next time you play.
Simpler to say square root of 5 units in any direction that lands in a square's center. In your 1 + rad 2, couldn't the knight diagonal back so that it was next to its original position? Knights surely exhibit some irrational behavior.
I wasn't aware that there was any real demand for a system to help remember how the knight moves. Isn't it already simple enough?
No kidding.
This is an amazingly active community for a topic like this to generate so many replies.