[Jeffhs]

I remember seeing ads for the Sylvania GT-Matic TVs when they were first introduced in the 1970s. Some of those sets had a control panel behind a front-panel door which could be locked after the controls were set to the viewer's liking. The TV owner kept the key; once the door was locked it was impossible to change the control settings. The TV probably had circuitry which monitored the picture, and would correct the settings if they drifted for any reason.

GE went one step further with its "VIR -- Broadcast Controlled Color" system, which used a signal in the vertical blanking bar to adjust and correct the color settings if necessary. However, one drawback of the GE "VIR" system was that the TV station or network to which the set was tuned had to be transmitting the VIR signal in the blanking interval; without that signal, the VIR system could not and did not work. I had a great-uncle who owned a GE VIR TV, but he never used the VIR function; in fact, I don't think he was even aware that his TV had the feature in the first place.