4 Monitoring and calculation of yearly and three-year rolling average
4.1 Monitoring
Monitoring shall be based on calculation of average sulphur content of residual fuels on the basis of sampling and testing by independent testing services. Every year the average sulphur content of residual fuels shall be calculated. After three years the reference value for monitoring will be set as described in paragraph 5.
4.2 Calculation of yearly average
At the basis of monitoring is the calculation, on an annual basis, of the average sulphur content of residual fuel.
The calculation of the average sulphur content is executed as follows:
For a certain calendar year, the sulphur contents of the samples analysed (one sample for each delivery of which the sulphur content is determined by fuel oil analysis) are recorded. The sulphur contents of the samples analysed are added up and divided by the number of samples. The outcome of that division is the average sulphur content of residual fuel for that year.
As a basis for well informed decisions a graphical representation of the distribution of the global sulphur content in residual fuels in terms of the % sulphur in increments of 0.50% sulphur plotted against the quantity of fuel associated with each incremental sulphur content range shall be made available by 31 January of each year.
The mathematical formula for the method of calculation described, is given in appendix 1 to this guideline.
4.3 Three year rolling average
A three year rolling average shall be calculated as follows:
Acr=(Ac1+Ac2+Ac3)/3
in which:
Acr = rolling average S-content of all deliveries tested over a 3 year period
Ac1,Ac2,Ac3 = individual average S-contents of all deliveries tested for each year under consideration
Acr is to be recalculated each year by adding the latest figure for Ac and deleting the oldest.
Setting of the reference value
5 The reference value of the world wide average sulphur content of residual fuel oils supplied for use on board ships shall be Aw, where Aw=Acr as calculated in January of the year following the first three years in which data were collected on the basis of these guidelines. Aw shall be expressed as a percentage.
