This series of six color-coded spring scales can be used for both force and mass measurements. Each scale is calibrated in both Newtons and grams or kilograms. The top is flat on one side so that the scale can b e used with an inclined plane. The scales incorporate a unique zero adjustment. The main feature is the clear plastic tube, which allows students to see the action of the spring. Grades 4 +. Set of 6 (250 g, 500 g, 1 kg, 2 kg, 3 kg, 5 kg)