Racing Rings consists of three rods one each of copper, aluminum and PVC, Ring magnet is dropped down the PVC rod, it falls unobstructed, Two metal rods create an induced magnetic field to that adds resistance to the rings travel, metals are different, they fall at different rates
Dry Field Mapping Kit, includes cork-covered base, 30cmx26cm; pad of 25 sheets pre-printed conductive paper 28cmx21.5cm; pad of 100 sheets preprinted paper for drawing fields; ten metal-headed push pins; a silver conductive pen