Yes, I want to use the right exchange rate to keep my accounts as accurate as possible, I'm only using the one fiat currency and that's Euro. I have it straight in my head now that the altcoin exchange rate doesn't matter, because that's predetermined by the amount of altcoin I end up with and the euro value I assigned to the Bitcoin "sale" on the other side of the transaction. I just need to establish the best method of calculating that euro value, whether that means taking the value from the original purchase price of BTC (probably too much room for manipulation since I could decide those are the coins I bought at 500 or 980 or anywhere in between
), the average purchase price of all my BTC (presently about 760) or from the exchange rate of the day (~840).I think you ought to be as honest as possible in calculating the original purchase price of BTC, otherwise it is not very meaningful to do your accounting.
Should not take the average unless you purchased the same amount of BTC every time.