Visual control is the use of visual information indicators to provide immediate feedback about a process so that anyone in the environment can understand what is going on. This technique is popular in a range of settings and in some cases is mandated by law for safety reasons. For example, emergency valves are clearly labeled, a form of visual control, to allow anyone to operate them and to make sure that bystanders are aware that the valves may vent suddenly and unexpectedly.
There are many forms of visual control. It may consist simply of posting operating instructions near a piece of equipment. It can also include indicator lights and status messages. Electronic systems commonly have a central control panel that provides information about what is happening in the system and where. It can generate error messages, highlight parts of the system that are in operation, and so forth. Examples can be seen in air traffic control rooms where radar monitors incoming aircraft and they are tagged with notes providing additional information.
When visual control is not present, only the operator knows what is going on, and she may not have an at-a-glance view of the whole system. Operators could know what is happening with the equipment they have responsibility for without knowing anything about the rest of the facility. They may not be aware of slowdowns and stoppages, for example. If the operator was incapacitated, another person would not be able to instantly take over without visual control, as that person wouldn't understand what was going on with the process.
Status boards can be useful for visual control. These are placed in a central location to allow supervisors and passersby to see what is happening in a facility. They may be electronic or could be updated manually. A printer, for example, might have a job board up showing what is assigned to each press, and providing information about the status of each job. She can move tags around on the job board, and each tag corresponds to a work ticket that can be consulted for more information.
To contrast visual control with other systems, it might help to think about walking into a kitchen where someone has stopped partway through preparing a cake. One baker has left out the recipe and all the tools and ingredients. It is easy to determine that the only remaining step is to mix wet and dry ingredients and put the cake in the oven. Another baker has not left out the recipe or any supplies. The baker taking over would have to guess what kind of cake was being made and what needs to be added to the batter before it can be baked.