Exchange rate of foreign income

I know that HMRC provides monthly rate, average rate and spot rate for foreign income. If I have 3 foreign incomes, can I use different exchange rate types for those 3 foreign incomes? or I have to use the same exchange rate type for all foreign incomes? Thanks.

Hi,
Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal. For your convenience, there are exchange rates here:
Exchange rates from HMRC in CSV and XML format
and for older rates here:
Foreign exchange rates and spot rates: 1 January 1989 to 31 March 2009
You are free to use any of the supplied rates or one of your own choosing. 
Thank you.