The measuring period number in which the sample has been collected shall be stated.
Each year (on or around 1 January) a new set of measuring periods will be stated.
When samples from several measuring periods are combined before analysis, the exact details of the mixing shall be stated in the Annex to the document with background information.
The number of the first measuring period shall be used to indicate the period for analysis (e.g. when the samples from period 9, 10, 11, and 12 are combined into a single sample for the analysis, this sample will be given the period number 9).