One electrode is not "negative". It is a Ground. Three electrodes are positive.
According to Hulda Clark :
“ parasites can be killed with a very small voltage. But only IF the voltage is 100% Positive Offset, and only IF the voltage is varied up and down repeatedly”.
“If the varying voltage become NEGATIVE, even momentarily, it supports and maintains their lives!
That explanation should make it clear why you want as many points on the body receiving positive pulses.