Another view of the headset, showing a marking band that identified the right-hand side of the headset. This was important, because the direction of the sound was determined by listening to the sound from one end of the C Tube in one ear, and the other in the other ear. Putting the headset on backwards would result in a 180-degree error.
C Tube hydrophone headset. Collection of Boyd A. Propert. Thanks to his son, David Propert for submitting the photo scan.