A rare device designed to test bone conduction. The tiny ear tube dissembles to reveal a metal disc which is held firm by two springs at either side. When inserted in the ear the small metal dumbbell is struck against the rim of the ear tube and causes the disk to vibrate.
The resulting bizarre twanging noise sounds more like something out of the ‘Magic Roundabout’. Whether or not this could quantify bone conduction is dubious – but it is nonetheless a superb little instrument!