When the voltage scale is changed, the Expand
function designates whether the signal expands
from the center of the screen or from the signal
ground level. Expand by center can be used to
easily see if a signal has a voltage bias. Expand by
ground is the default setting.
If the vertical scale is changed when the Expand
function is set to ground, the signal will expand
from the ground level*. The ground level does not
change when the vertical scale is changed.
If the vertical scale is changed when the Expand
function is set to center, the signal will expand
from the center of the screen. The ground level will
suit to match the signal position.
*Or from the upper or lower edge of the screen if
the ground level is off-screen.