For centuries speed sensors have been used to determine the speed of moving objects. In fact, the very first primitive speed sensors were lengths of rope with a knots tied in them that were tossed over the sides of moving ships to determine how many “knots” the ship was traveling at. However; the advent of the motorized wheeled carriage created the need for a more advanced mechanical speed sensor, such as the type that used a gear and a cable » Read more: How Does a Magnetic Speed Sensor Work