To find the equivalent, the Norton current I no is calculated as the current flowing at the terminals into a short circuit (zero resistance between A and B). This is I no. The Norton resistance R no is found by calculating the output voltage produced with no resistance connected at the terminals; equivalently, this is the resistance between the terminals with all (independent) voltage sources short-circuited and independent current sources open-circuited. This is equivalent to calculating the Thevenin resistance.