I am currently building an energy monitor according the the specifications of this site,http://openenergymonitor.org/emon/node/59. I understand how the current is measured but I am confused by the voltage measurement circuit. I do not understand how the step-down adapter can correctly measure voltage usage from one outlet. I understand that the lights and outlets are in series but I was reading that typically dryers and air conditioners are typically on a separate circuit. So how can the voltage used from these appliances be measured from the one outlet? Thanks.