The system will, in general, operate without any need to communicate with the user. However, the configuration procedure at the user site must determine the parameters for converting magnetic unit polar coordinates to the video image screen coordinates.
It is important to make this easy for the user to do. The users need to feel comfortable moving system components around to meet their needs. They also need to check the parameters quickly whenever a component might have been knocked out of alignment.
Although keyboard and mouse have shown themselves to be effective user input devices for a desktop situation, they are limiting when embedded in an open area setting. Keyboards are very hard to use when an ergonomic position cannot be achieved and maintained, as is usually the case if the user cannot sit down. Mice require a flat surface to operate and most variants do not survive a dirty industrial environment well. Thus, a user interface that requires these devices (or emulations thereof) is usually inconvenient to the users.
A standard Linux system does not have a single native user interface model, so we are free to select user input and output devices to suit our environment and needs. A joystick (whether analog or USB) was found to be a sufficient input device, while a VCR-style `On Screen Display' met our output device needs.
Suitable joysticks
are cheap and can be picked up for 
or so. There
is less of a problem with damage, loss or theft compared
to handheld keyboards and clip-on mice with 
prices.
The hot-plug capabilities of USB are also helpful.