The instrument
By the 1940s DuMont was the leader in the oscilloscope equipment market.The Oscillator Type 348 appeared on the market around 1955.
Details
DuMont was one of the earliest designers of the triggered sweep oscilloscope using a gas thyratron vacuum tube (forerunner to the silicon controlled rectifier or SCR). This allowed the oscilloscope to display a visual trace at a preset input signal level. In addition the sweep (trace across the CRT screen) could be regulated by the sweep speed or sweep frequency. This design allowed the oscilloscope to provide better visual detail of the signal being studied. The trigger was a frequency synchronizing type which provided viewing stability.
(source: wikipedia