Pair of headphones, part of Dr. Richard Sloan's Zero Gradient Aural Thermometer system
1975-1985
Zero-Gradient Aural Thermometer system invented by Dr. Richard Sloan, England: comprising a pair of headphones, made by Amplivox Ltd., Oxfordshire, England and MRC EPU Model No. 8151.1, Serial No. A4000 made by Addison Process Control Ltd., Beckenham, Kent, England, 1975-1985. This Zero-Gradient Aural Thermometer system was used by Dr. K. J. Collins, England.