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

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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]