§ 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.