Thanks Daniel - no that was not what I meant.
What I meant might be illustrated by imagining having a foreign currency bank account, say sterling, with numerous debit/credit entries during the year.
Now suppose you make one particular withdrawal, and you need to calculate the historical GBP/EUR exchange rate at which those GBP funds were originally obtained in GBP. In other words you need to work out which GBP lodgements into that bank account made up (on a FIFO basis) the funds being withdrawn, and the exchange rates attributable to each of those lodgements. From this you caculate whether you made a CGT gain or loss in EUR on the GBP funds being withdrawn. If you have a small number of transactions this is not a problem, but with many transactions it is complete PITA. I am looking for some way of automating it.