What is the Ben System, in brief?

An advanced system (Ben Pridmore's) that maps larger chunks — three digits or a pair of cards — to a single rich image, for extreme compression.

Beyond PAO lies further compression: the Ben System encodes three digits (or two cards) as one image using a structured scheme, so a single picture carries even more than a PAO slot. It's powerful but demanding to build and drill (roughly a thousand images), used by elite competitors chasing records. You don't need it to benefit hugely from plain PAO — it's the far end of the same idea: more items per image.

Go deeper:

• Ben Pridmore (Wikipedia) — documents the two-cards/three-digits-to-one-word system exactly.