1. The operator shall determine the activity data of a source stream in one of the following ways:

(a) on the basis of continual metering at the process which causes the emissions;

(b) on the basis of aggregation of metering of quantities delivered separately, taking into account relevant stock changes.

2. For the purposes of point (b) of paragraph 1, the quantity of fuel or material processed during the reporting period shall be calculated as the quantity of fuel or material received during the reporting period, minus the quantity of fuel or material moved out of the installation, plus the quantity of fuel or material in stock at the beginning of the reporting period, minus the quantity of fuel or material in stock at the end of the reporting period.

Where it is technically not feasible or would incur unreasonable costs to determine quantities in stock by direct measurement, the operator may estimate those quantities on the basis of one of the following:

(a) data from previous years correlated with output for the reporting period;

(b) documented procedures and respective data in audited financial statements for the reporting period.