This apparatus is used to demonstrate and teach the basic principle of an electric meter. Apparatus consists of a 3.75" (90mm) dia. air coil wound on an acrylic tube with an acrylic plate in the center to hold a compass. The coil has multiple tappings of 50, 100 and 200 turns, and also has a built-in potentiometer for varying the current, these features allow multiple readings. Operates on one "AA" battery (not included). Includes one compass. Base 7.34" (195mm) x 4.75" (120mm) x 0.5" (12mm). Total height 4.25" (110mm).