Obviously, the popularity and desirability of Klein bottles follow a curve shaped like a Klein bottle. We're currently in the main volume stage, and will loop back through over the next few years.

You should graph your previous sales history. It will almost certainly be indicative of future sales ;-)

P.S. We really do love you Cliff, thanks for being you!

I very rarely comment, but I just wanted to say thanks for being awesome!

After showing my mum the video you did with Numberphile, she bought me one of your Klein bottles for my birthday. It's still one of my favourite nonorientable surfaces. ;)

All the best,

James