How does PAO memorise long numbers?

With a 00–99 PAO, read six digits per image — first pair = Person, second = Action, third = Object.

* Six digits become one scene: pairs 15/27/38 map to Person/Action/Object at one locus. *

Exactly like cards, but the "items" are 2-digit numbers. Chunk the number into sixes: 15 27 38 → Person 15, Action 27, Object 38 → one composite. Place composites along a palace and you can hold hundreds of digits with a manageable number of images. This is the standard competitive method for the "spoken numbers" and "numbers" disciplines — six digits per locus instead of one or two.

Go deeper:

• Nelson Dellis — How to create a 2-digit PAO system — building the 00–99 PAO that reads six digits per image.
• Numeric PAO (Wikipedia) — the six-digits-per-image example.