Seventy years ago, this employee of Bogue Electric Manufacturing Company of Paterson, NJ, is making some finishing adjustments on the model SL-102 sonic liquid level indicator.

The instrument met a long standing industrial need for accurate level gauges in tanks, free from floats and other moving parts. The system was both safe and explosion-proof. The system was able to automatically compensate for differences in pressure and temperature, and was even able to read the interface level of two liquids in the same tank.

The photo appeared on the cover of Radio News, June 1954.