Cruise control also known as speed control or Auto control is a system that automatically controls the rate of motion of a motor vehicle. The driver sets the speed and the system will take over the throttle of the car to maintain the same speed.
This system calculated ground speed based on driveshaft rotations and used a solenoid to vary throttle position as needed.

In modern designs, the cruise control may or may not need to be turned on before use — in some designs it is always ON but not always enabled, others have a separate "on/off" switch, while still others just have an ON switch that must be pressed after the vehicle has been started. Most designs have buttons for set, accelerate, and coast functions. Some also have a cancel button. Alternatively, tapping the brake will disable the system, a required feature to prevent the vehicle from accelerating against braking as it attempts to maintain speed.

Dear friends if you have nay kind of query about auto control or any car related issue please post here your kind response.