This study shows the effective exchange rate and is a measure of  the value of a currency against a `basket’  of other currencies, relative to a base date. It is calculated as a weighted geometric  average of the exchange rates, expressed in the form of an index. The effective  exchange rate indices for sterling and other currencies published by the Bank are based  on the method the IMF uses to calculate  effective exchange rates for a number of  industrialized countries.

The weights used  are designed to measure, for an individual  country, the relative importance of each of the other countries as a competitor to its  manufacturing sector. The trade weights  reflect aggregated trade flows in  manufactured goods for the period 1989 to  1991 and cover 21 countries. The base date for the index is 1990, and is set at 100.

Getting back to the 10-year moving average will not be to tough, although the Yen has rejected the 100 level a few times over the last weeks. At this point, it would not be too difficult to see that 100 is in the near future and then a bounce back as the recent slope has been quite dramatic.