James:

Maybe I still am not doing it right.

When I touch to resume it resets.
(It is also “locked” in portrait mode)

When I zoom in the scale changes as expected. However, what I would usually want to do is zoom out so the scale starts from zero (imitating an oscilloscope). This would give a realistic overall view of the voltage.

(I have a pet peeve with graphs that have no zero)

Tom