47 CFR § 73.258 - Indicating instruments.
(a) Each FM broadcast station shall be equipped with indicating instruments which conform with the specifications described in § 73.1215 for determining power by the indirect method; for indicating the relative amplitude of the transmission line radio frequency current, voltage, or power; and with such other instruments as are necessary for the proper adjustment, operation, and maintenance of the transmitting system.
(b) The function of each instrument shall be clearly and permanently shown in the instrument itself or on the panel immediately adjacent thereto.
(c) In the event that any one of these indicating instruments becomes defective when no substitute which conforms with the required specifications is available, the station may be operated without the defective instrument pending its repair or replacement for a period not in excess of 60 days without further authority of the FCC: Provided that, if the defective instrument is the transmission line meter of a station which determines the output power by the direct method, the operating power shall be determined by the indirect method in accordance with § 73.267(c) during the entire time the station is operated without the transmission line meter.
(d) If conditions beyond the control of the licensee prevent the restoration of the meter to service within the above allowed period, an informal letter request in accordance with § 73.3549 may be filed with the FCC, Attention: Audio Division, Media Bureau, in Washington, DC for such additional time as may be required to complete repairs of the defective instrument.