As you may have gathered, there are many variations on the anglo system and many key combinations. In these charts I have decided to show only the most common layouts, but I am breaking my rule for this ingenious system. It was devised by the concertina makers Harold Herrington and Frank Edgley as a way of proucing lightweight concertinas that are optimised for Irish music but are also largely chromatic. The core is the same as a 20-button C/G, but note the 3 extra C#'s, to help play the key of D, and the scattering of other accidentals.
This chart was prepared by David Gray, and is used by permission.