A grumpy old device designed to dampen the seats in small corners of large aeroplane flight decks. Astonishingly, some very old aeroplanes even carried more than one of the breed; others also carried a variety of teenage wireless operators....plus a mumbling old fart to keep an eye on the dilithium crystals.
Never met a pilot who could fly an instrument approach better than one advised by a nav.
Despite what the voices in a pilots 'mind' head might say.