This little robot follows a black line drawn on a white background. How did we do it? The two (black) Distance Sense Cubelets change the speed of their associated (clear) Drive Cubelets, causing the robot to turn when one of the Sense Cubelets begins to cross the line. The (green) Blocker Cubelet in the middle keeps the signals from the Sense Cubelets separate, and the Knob Cubelet on top allows for tuning the robot's sensitivity. The two Bar Graph Cubelets on each side aren't strictly necessary but they make it look more like a robot, and they do show what's going on.