Just trying to get the above straight as I would like to determine the amps used by my home theatre system: I know that amps x volts = watts. Now I do own a Radio Shack meter and also purchased a amp probe to go with the meter. I made my own single wire adapter as I could not find one at Radio Shack. I put in a 100 watt bulb in a lamp and measured the amp. The amp came out to 0.7 amps. I thought that a 100 watt bulb on a standard 120 volt circuit should yield 0.83 amp usage (ie. 100 watts/ 120 volts = .83 amps)??? why 20% difference? Is this correct??? ( I did check my voltage and it read 118.6 volts which actually will make the difference a little more). Could the difference be due to too much plastic around the measuring wire (I basically used a three prong electrical wire and separated one of the wires (non-ground). Is their a difference if I where to measure the neutral vs the positive?