A thick line drawn on a sheet of paper with a 6B pencil is electrically conductive and its resistance can be roughly estimated using a simple tester made of a light-emitting diode (LED) and a lithium coin-type cell. Using this hand-drawn resistor and the LED tester, we developed teaching materials that help students to understand how electrical resistance varies according to (a) the length of resistant lines, (b) the width of resistant lines, (c) the number of resistant lines and (d) the type of connection between resistant lines. (Contains 2 tables and 8 figures.)