Each emitter projects infrared light onto the floor. The amount of light reflected back from the dark line differs from that reflected from the floor; thus it can tell where the dark line is.

Mr. Line comes in kit form, allowing the user to more fully understand robotic structure and functionality. Although relatively simple to assemble, Mr. Line is highly functional and is quite "smart". Information travels from the sensors to the CPU and then to the motors for steering. By including a CPU in Mr. Line's construction, the robot is able to make constant course corrections, search for the line if it is knocked off course, and handle the cross over involved in a "figure 8" course layout.

Mr. Line is a line-tracing robot. It follows a path laid out for it along a floor or other smooth surface. The path must be a dark line on a light background.

Mr. Line has three pairs of infrared emitters and receivers. One pair is on the left, another in the middle and the third on the right.