Oscilloscopes have always had some dead time after completing a trace when they were not able to be retriggered.
I noticed a hand held DSO that I was evaluating to produce a different result on a train of pulses that repeated every 10m, different to a budget Tek TDS2024C DSO.
So, I have conducted an experiment comparing 7 DSOs that I can put my hands on.
The test waveform is a burst of 1MHz 50% square wave of adjustable number of cycles n, and the burst repeated every 100ms.
Setting the DSO timebase to 1µs/div and NORMAL trigger, and with zero time at mid display, the initial display with n=10 is a flat line up to mid screen, then pulses (5 or 6 depending on the display width) to edge of screen. This is rewritten every 100ms with every new burst.
If n is increased, eventually n is large enough that the timebase will be retriggered within the same burst, and this critical value of n gives insight into the dead time.
Above is a table of results.
The dead time under this test is applicable to the test scenario, and may be different for other timebase rates.