Pilot fish gets a panicked phone call from the central control supervisor at a busy international airport. The VT420 dumb terminals are double-displaying every character typed, so that “exit,” for example, is being displayed as “eexxiitt.” Of course, when users hit Enter after typing “exit,” they get an error message regarding the unknown command “eexxiitt.”
The terminals are used to enter commands to do things such as starting up and shutting down the central control software — thus the panic.
Fish takes a look and sees that there’s a setup menu that lets you control the behavior of the terminal. One of the menu options — about three levels deep — is “Turn on Local Echo.” The sole purpose of Local Echo is to repeat each character typed on the keyboard.
Source: Enterprise Applications