Eric DeGroot's Price Diffusion Index - anyone know how to calculate?

Hi Everyone,

Greetings! I hope everyone is having a fine weekend!

I've looked everywhere for how to calculate a gold price "diffusion index" similar to what Jim Sinclair and Eric de Groot show at their websites on various gold and silver price charts. For example, take a look at this entry on Eric's website where he show's the price of silver along with a diffusion index (of price?):

https://edegrootinsights.blogspot.com/2012/09/wait-until-fish-are-biting...

I'm curious: does anyone know how this "diffusion index" is actually calculated? I've looked on them internets for a bit, but can't find a reasonable answer, so I now humbly ask the Turdite community for any assistance.

Thank you very much for any assistance you can provide. Take care!

Stephen