This Soundor capillary gauge dates from about 1954 where it could be seen in the US Divers catalog for about $1.20.  The gauge was very fragile and as a result not many last to this day.  This gauge was also sold with the Australian Porpoise regulator set in the 50s.  Many diver would glue these gauges to their homemade film camera housing to be sure of depth which was very important for colour absorption.