The window is how much time the plot shows. Every row shares one window: the figure has a single x link group, so the rows cannot drift apart. The trigger's event span follows it, and the pre-trigger share is a share of this window.
The header bar's window button opens a popover: type a number, pick a unit under it, or step a decade with the arrows.
The button's own label is a reading of the current window in a natural unit, width-locked so a change of window cannot widen the header bar.
A window too long to store at the wire rate is decimated, not refused. The shared clock takes a power-of-two stride, and each group of samples is averaged rather than strided, so a tone above the stored Nyquist is attenuated instead of aliasing to a false low frequency.
The stamp stored for a group is the group's mean, which is where the averaging puts the value. Stamping at the end of a group would shift every trace half a stored sample late.
Moving the window across a decimation boundary rebuilds the buffer and drops the history. Walking it inside one decade is free.
This control is the only thing that changes the window. A zoom, a pan or a fit moves the view inside it and leaves it alone — which is the point of the previous bullet: a wheel notch that redefined the window could re-plan the buffer and throw your samples away.
The trigger sees the stored (filtered) signal, not the wire signal, because an edge found on a sample that is not in the buffer could not be cut out of it.
1 MS/s with the default buffer of 8 388 608 samples per signal (8.39 s). A 2 s window
stores every sample (time x1). Widen it to 600 s and the stride becomes
x128: 7.8 kS/s stored, anti-aliased at 3.9 kHz. A 5 kHz sine seen through that
window is attenuated by the filter, not folded down to a full-amplitude low-frequency one.