4 A reference line is defined as a curve representing
an average index value fitted on a set of individual index values
for a defined group of ships.
5 One reference line is developed for each ship
type to which regulation 21 of MARPOL Annex
VI is applicable, ensuring that only data from comparable ships
are included in the calculation of each reference line.
6 The reference line value is formulated as Reference
line value = a (100% deadweight) -c
where "a" and
"c" are parameters determined from the regression curve fit.
7 Input data for the calculation of the reference
lines is filtered through a process where data deviating more than
two standard deviations from the regression line are discarded. The
regression is then applied again to generate a corrected reference
line. For the purpose of documentation, discarded data is listed with
the ships IMO number.