The Kerr Symballophone, c. 1940 was very similar to Alison's differential model, but used two diaphragm chest pieces rather than bell chest pieces. In addition, sounds from either chest piece could be heard in both ears so that the examiner could compare sounds emanating from different parts of the chest. On the left is the Kerr Symballophone, c. 1940. Note the metal chest pieces and close-up of the double-looping tube connections of the binaural earpieces, such that each ear could hear the sound from either chest piece. On the right is an example of the Symballophone, c. 1950s. Note that the chest pieces are now made of light weight Bakelite instead of metal and that the rubber tubes are very long, presumably so that disparate parts of the chest could be auscultated and compared. A document describing the use of the symballaphone that came with each stethoscope. This stethoscope was used by Dr. William Faulkner (1896-1976), a thoracic surgeon who was at UCSF during the tenure of Dr. Kerr's leadership of the UCSF Department of Medicine.