The 1/3 octave band analysis program SX-A1RT for the RIONOTE Multifunction Measurement System supports measurement of the NC value.
The illustration below shows the concept of a system using a microphone installed indoors to measure the NC value.
Normally, the octave band analysis values from 63 Hz to 8 kHz have to be read and applied to the NC curve, and the values below the limit for all points are then used to determine the NC value.
With the SX-A1RT on the other hand, the octave band analysis results are used to automatically calculate the NC value, making the process much more convenient.

NC (Noise Criteria) are a way to determine the room environmental sound level based on the following reference.
L.L.Beranek（ed） : Noise and vibration control. McGraw-Hill Book Company, New York, 1971