Strutt|Criteria|Ratings|Absorption|NRC calculates the Noise Reduction Coefficient (NRC) of the current row of the worksheet
In an octave band sheet, NRC is calculated as:
`NRC=(alpha_(250)+alpha_(500)+alpha_(1k)+alpha_(2k))/4`, rounded to the nearest 0.05
In a 1/3 octave band sheet, NRC is calculated as:
`NRC=(alpha_(200)+alpha_(250)+alpha_(315)+alpha_(400)+alpha_(500)+alpha_(630)+alpha_(800)+alpha_(1k)+alpha_(1.25k)+alpha_(1.6k)+alpha_(2k)+alpha_(2.5k))/12`, rounded to the nearest 0.05
where:
`alpha_(x)` is the absorption coefficient in each octave or 1/3 octave band.