The transmitter transmits first from left then from right to one end of the ruler. Then the same for the other end to form the two triangles shown. From this event all the lengths of the two triangles sides can be found. With the cosine rule, the two triangles can then be resolved in terms of all their angles and from this the position and angle of the ruler can be calculated and sent to the ruler's display. A further complication is that the ruler must also use electromagnetic radiation (eg radio) to fulfill this task.