47 CFR § 73.754
Frequency monitors
February 16, 2021
(a) The licensee of each international broadcast station shall operate a frequency monitor at the transmitter independent of the frequency control of the transmitter.
(b) The frequency monitor shall be designed and constructed in accordance with good engineering practice. It shall have an accuracy sufficient to determine that the operating frequency is within one-half of the allowed tolerance.
[37 FR 25842, Dec. 5, 1972]