47 CFR § 1.19
Use of metric units required
February 16, 2021
Where parenthesized English units accompany metric units throughout this chapter, and the two figures are not precisely equivalent, the metric unit shall be considered the sole requirement; except, however, that the use of metric paper sizes is not currently required, and compliance with the English unit shall be considered sufficient when the Commission form requests that data showing compliance with that particular standard be submitted in English units.
[58 FR 44893, Aug. 25, 1993]