According to Wikipedia
A voltage doubler is an electronic circuit which charges capacitors from the input voltage and switches these charges in such a way that, in the ideal case, exactly twice the voltage is produced at the output as at its input.
NOTE: Do not confuse with Function generator CH1 not being grayed out. It is unselected. (see the CH0 radio input)
You can see it. math channel
M0 = CH0 + CH1 is the output of voltage doubler.