Strutt|Criteria|Ratings|Absorption|NRC calculates the Noise Reduction Coefficient (NRC) of the current row of the worksheet.
In a 1/3 octave band sheet, the NRC rating is calculated as follows (in accordance with ASTM C634):
`NRC=(alpha_(250)+alpha_(500)+alpha_(1k)+alpha_(2k))/4`, rounded to the nearest 0.05
where:
`alpha_(x)` is the absorption coefficient in each 1/3 octave band.
In an octave band sheet, NRC is calculated as follows (this is NOT in accordance with ASTM C634 and is provided for reference only):
`NRC=(alpha_(250)+alpha_(500)+alpha_(1k)+alpha_(2k))/4`, rounded to the nearest 0.05
where:
`alpha_(x)` is the absorption coefficient in each 1-octave band.