BS EN ISO 4871:2009

1   Scope This International Standard

— gives information on the declaration of noise emission values,

— describes acoustical and product information to be presented in technical documents for the purposes of noise emission declaration, and

— specifies a method for verifying the noise emission declaration.

It is applicable to machinery and equipment. 
The values to be used for the purposes of noise emission declaration are either declared
  single-number noise emission values,  L  d , or declared dual-number noise emission values,  L  and  K. L  is a noise emission value determined directly from measurements and  K  is the uncertainty associated with those measurements.  L  d  is the sum of  L  and  K  and represents an upper limit which values from repeated measurements are unlikely
  to exceed at a given confidence level;  L  d  corresponds to the stated or labelled value,  L  c , defined in [ISO 7574‑1](/search?q=ISO%C2%A07574%E2%80%911). 
The two forms of noise declaration are alternative means of representing any or all
  of the A-weighted sound power level,  L   w   A , the A-weighted emission sound pressure level at specified positions,  L p   A  and the C-weighted peak emission sound pressure level at specified positions,  L p   C,peak . The choice ...