Extremely versatile kits for teaching about electrical resistance and resistivity.  Draw a pencil line across the unit, study the LED brightness. Then make the line thicker. What happens? Draw a second line in parallel. Change the length of the lines. Change the thickness (height) of the line. Can be used to compare conductors and insulators including the entire class. ERIC (Electrical Resistance in the Classroom) is the original kit. New BERT (Battery Electrical Resistance Tester) can also be used to test the conductivity of liquids. Both kits include PP3 battery, Crocodile clip lead, eraser, HB pencil and comprehensive instructions.