§  73.1215   Specifications for indicating instruments.

   The following requirements and specifications shall apply to indicating
   instruments used by broadcast stations:

   (a) Linear scale instruments:

   (1) Length of scale shall not be less than 2.3 inches (5.8 cm).

   (2) Accuracy shall be at least 2 percent of the full scale reading.

   (3) The maximum rating of the meter shall be such that it does not read
   off scale during modulation or normal operation.

   (4) Scale shall have at least 40 divisions.

   (5) Full scale reading shall not be greater than five times the minimum
   normal indication.

   (b) Instruments having square-law scales:

   (1) Meet the requirements of paragraphs (a) (1), (2), and (3) of this
   section for linear scale instruments.

   (2) Full scale reading shall not be greater than three times the
   minimum normal indication.

   (3) No scale division above one-third full scale reading shall be
   greater than one-thirtieth of the full scale reading. (Example: An
   ammeter meeting requirement (1) having full scale reading of 6 amperes
   is acceptable for reading currents from 2 to 6 amperes, provided no
   scale division between 2 and 6 amperes is greater than one-thirtieth of
   6 amperes, 0.2 ampere.)

   (c) Instruments having logarithmic scales:

   (1) Meet the requirements of paragraphs (a) (1), (2), and (3) of this
   section for linear scale instruments.

   (2) Full scale reading shall not be greater than five times the minimum
   normal indication.

   (3) No scale division above one-fifth full scale reading (in watts)
   shall be greater than one-thirtieth of the full scale reading.
   (Example: A wattmeter meeting requirement (3) having full scale reading
   of 1,500 watts is acceptable for reading power from 300 to 1,500 watts,
   provided no scale division between 300 and 1,500 watts is greater than
   one-thirtieth of 1,500 watts or 50 watts.)

   (d) Instruments having expanded scales:

   (1) Shall meet the requirements of paragraphs (a) (1), (2), and (3) of
   this section for linear scale instruments.

   (2) Full scale reading shall not be greater than five times the minimum
   normal indication.

   (3) No scale division above one-fifth full scale reading shall be
   greater than one-fiftieth of the full scale reading. (Example: An
   ammeter meeting the requirement (1) is acceptable for indicating
   current from 1 to 5 amperes, provided no division between 1 and 5
   amperes is greater than one-fiftieth of 5 amperes, 0.1 ampere.)

   (e) Digital meters, printers, or other numerical readout devices may be
   used in addition to or in lieu of indicating instruments meeting the
   specifications of paragraphs (a), (b), (c), and (d) of this section.
   The readout of the device must include at least three digits and must
   indicate the value of the parameter being read to an accuracy of 2%.
   The multiplier, if any, to be applied to the reading of each parameter
   must be indicated at the operating position.

   (f) No instrument which has been broken or appears to be damaged or
   defective, or the accuracy of which is questionable shall be used,
   until it has been checked, and if necessary repaired and recalibrated
   by the manufacturer or qualified instrument repair service. Repaired
   instruments shall not be used unless a certificate of calibration has
   been provided showing that the instrument conforms to the
   manufacturer's specifications for accuracy.

   [ 41 FR 36818 , Sept. 1, 1976;  41 FR 43152 , Sept. 30, 1976, as amended at
    51 FR 2707 , Jan. 21, 1986]