The reflectance sensors are important to the completion of the AEV because it counts the times the wheel turns and allows the programmers to gauge the distance the AEV has traveled. The sensors lie against a wheel marked with four alternating sections of silver and black and each time the sensors detect a change in color the code interprets that as a certain distance traveled. The second sensor allows the program to detect which direction the wheel is turning and give the programmer greater control of the AEV.