Sure it isn't hard to figure out the denomination of a given bank note, but that's not what I'm talking about. If I shuffle the notes in your wallet and tell yo

Sure it isn't hard to figure out the denomination of a given bank note, but that's not what I'm talking about. If I shuffle the notes in your wallet and tell you to get a 20 out, you'll have to go through them one by one. If you do the same with mine, I go for the medium sized blue note. Related: how do blind people distinguish dollar notes? I know a blind guy who recognises euro denominations by their size very reliably.