BABY BOOMER ALERT: “Parkit Dial”…..What the Heck Is This??

I will admit, at first I was very curious about this "driving aid."  But the more I looked this odd gadget, the more I read..well, I just cannot figure out how it worked!  Apparently it was sold in the 1950s to "take the work and worry out of parking a car."  Well, thanks...but WHAT IS THIS??

Anybody got a clue?