Sec.  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]