Like input-output symbols, process boxes have a single line connecting it to the previous flowchart step and a single line leading to the next one. A flowchart may contain any number of process boxes.

A flow chart ... process or system. It begins with the input of data or materials into the system and traces all the procedures needed to convert the input into its final output form.

However, the simple flow chart of Input, process, and output are still used to visualise how the system performs. With mechanical control systems the input is supplied by movement, this is known ...