Proportional control means that the output of a system is directly related to the input. System inputs include both a target value, which is the desired result such as a specifice position, pressure, or force level, and the real-time measurement of actual progress toward that goal. With proportional control, the output of a system can be any interim value within a fixed range. For example, an air cylinder can be positioned anywhere between fully retracted and fully extended. In another example, a tank's pressure can be maintained anywhere between vacuum and full line pressure. Proportional control is a cost effective way to create systems with high flexibility and dynamic control.