The effective exchange rate index is a chain-linked index. Percentage changes in the index are calculated by comparing the change in the index based on consumer prices for the country concerned (expressed in US dollars at market exchange rates) to a weighted average of changes in its competitors' indices (also expressed in US dollars), using the weighting matrix of the current year. The indices of real effective exchange rates are then calculated from a starting period by cumulating percentage changes. This gives a set of real effective exchange rates based on moving weights. The series are updated continuously.