For the determination of a measurement value, the following sampling methods may be used:
1° 
continuous sampling during the full reference period; 

2° 
sampling during a number of consecutive onehour intervals covering the full reference period; with this, the measurement value corresponding to the reference period considered is calculated as the timeweighted arithmetic mean of the various measurements; 

3° 
discontinuous sampling, during the reference period, whereby the sampling duration of the various sampling operations may vary by no more than a factor of 2. In that case, depending on the sampling duration used, at least the following number of samples shall be taken: 

a) 
for a 1hour reference period:



b) 
for reference periods that last more than 1 hour:

If necessary, the sampling duration or frequency must be increased if the indicated sampling duration or frequency does not suffice to obtain a reliable end result.
The reference period may be split into different periods of at least 1 hour if required to obtain a representative end result.
The person carrying out the measurements shall check that the chosen sampling duration and measuring frequency and, where applicable, the splitting up in time provide a representative average for the stipulated reference method.