Hello,
It looks like an oscilloscope.
The first oscilloscopes did not have a trigger function and had a free running oscillator as timebase.
The trick was to adjust the frequency knob to have a steady picture on screen.
From the wiki:
Synchronized sweep
Oscilloscope with synchronized sweep. "HOR. SELECTOR" sets horizontal frequency range (the capacitor); "FREQ. VERNIER" adjusts the free-running frequency; "SYNC. AMPLITUDE" sets the gain to the comparator.
Early oscilloscopes used a synchronized sawtooth waveform generator to provide the time axis. The sawtooth would be made by charging a capacitor with a relatively constant current; that would create a rising voltage. The rising voltage would be fed to the horizontal deflection plates to create the sweep. The rising voltage would also be fed to a comparator; when the capacitor reached a certain level, the capacitor would be discharged, the trace would return to the left, and the capacitor (and the sweep) would start another traverse. The operator would adjust the charging current so the sawtooth generator would have a slightly longer period than a multiple of the vertical axis signal. For example, when looking at a 1 kHz sinewave (1 ms period), the operator might adjust the horizontal frequency to a little bit more than 5 ms. When the input signal was absent, the sweep would free run at that frequency.
If the input signal were present, the resulting display would not be stable at the horizontal sweep's free-running frequency because it was not a submultiple of the input (vertical axis) signal. To fix that, the sweep generator would be synchronized by adding a scaled version of the input the signal to the sweep generator's comparator. The added signal would cause the comparator to trip a little earlier and thus synchronize it to the input signal. The operator could adjust the synch level; for some designs, the operator could choose the polarity.
[13] The sweep generator would turn off (known as blanking) the beam during retrace.
[14]
The resulting horizontal sweep speed was uncalibrated because the sweep rate was adjusted by changing slope of the sawtooth generator. The time per division on the display depended upon the sweep's free-running frequency and a horizontal gain control.
A synchronized sweep oscilloscope could not display a non-periodic signal because it could not synchronize the sweep generator to that signal. Horizontal circuits were often AC-coupled
https://en.wikipedia.org/wiki/Oscilloscope_history
Bertus