the atb diff is, put very simply, the same mecahnical theory mechanism as you'll find in a stud extractor

there are a few bits of metal that progresvily lock with each other the more you turn them against each other, but while they are both turning at the same rotational speeds there is no locking action

but wheel up in the air scenarios make them send all the power to the wheel that has no drive, trange that

also, as far as i was aware, it's not a quaife orignial design as maserati used the same diffs on their cars from at least the early 80's (was speaking to a marerati anorak a good few years ago who had techincal drawings of all the various components he had on his car, exploded diagrams and all that "only nerds love this" type of paraphinaliay )