16 CFR § 410.1 - The Rule.
In connection with the sale of television receiving sets, in commerce, as “commerce” is defined in the Federal Trade Commission Act, it is an unfair method of competition and an unfair and deceptive act or practice to use any figure or size designation to refer to the size of the picture shown by a television receiving set or the picture tube contained therein unless such indicated size is the actual size of the viewable picture area measured on a single plane basis. If the indicated size is other than the horizontal dimension of the actual viewable picture area such size designation shall be accompanied by a statement, in close connection and conjunction therewith, clearly and conspicuously showing the manner of measurement.
For the purposes of this part, measurement of the picture area on a single plane basis refers to a measurement of the distance between the outer extremities (sides) of the picture area which does not take into account the curvature of the tube.
Any referenced or footnote disclosure of the manner of measurement by means of the asterisk or some similar symbol does not satisfy the “close connection and conjunction” requirement of this part.
“Brand Name 21.”
The numbers in parentheses reflect the metric equivalent of the English measurements. They are provided for information purposes only, and are not required to be included in the disclosures.