This is for audio equipment with two-prong AC plugs, and the prongs the same width. No longer made. Connect this device from the chassis ground of a piece of audio equipment to the ground of a wall socket. Try the AC plug one way, then reversed. This device will let you know which position is correct. Also can be used with DVD decks having non-polarized female receptacles on detachable AC power cords. Has memory. With new 9V battery. No manual but one not needed. One minor scratch, otherwise perfect condition. See photo. I will pay for shipping USPS Priority Mail in continental U.S.. Asking $35.00. (Some have been online as high as $70.) From Zip 97223.