It's surprisingly easy once you get the hang of it. I started counting in dozenal for fun, and now when I think "7, 8, 9" my brain finishes the series with "X,

It's surprisingly easy once you get the hang of it. I started counting in dozenal for fun, and now when I think "7, 8, 9" my brain finishes the series with "X, E, 19". It's not common enough to use with other people, but I use dozenal in my personal projects and journal whenever possible.