Some of the image links have gone, but the descriptions are still clear enough and his vids are informative.
So, there's two pots with a centre detent. One is a 250k pot from 0 to 5, then it goes open-circuit from 5-10. The other is low resistance 0-5, then goes to 1M from 5-10.
Here's the bit I liked: The writer posted a diagram of how to rewire this pot to do treble cut 5 to 0, no load at 5, bass cut 5 to 10. That's about all you could want from a single tone control. Clever I think!