The peak to peak vaule of Spooky settings is 20V,
it is the range between the minimum(-10V) and maximum(+10V).
Such as sine wave,the wave crest to wave Hollow is -10V to +10V,
so peak-to-peak value is 20V p-p.
It is highly recommended not to use a multimeter. If you insist on using it, set the measurement frequency at 50hz.
You could test out RootMeanSquare by using multimeter, it is not able to test out peak-to-peak value.
For the second picture, the setting of frequency is zero, so the output is DC signal, -10v is normally.
The voltage amplitude is correct. Please no worries.