On the TDS200 series how does dual timebase work?

On the TDS200 series how does dual timebase work?

From the Horizontal Menu, select "Window Zone". Two vertical bars will be displayed, showing the zone to be expanded.

Use the Horizontal Position control to set zone position. Use Time/Div to set zone duration.

Main(M) and Window(W) time/div readouts are below the graticule area.

Select "Window" to display the Window timebase.