Fathom sources historical exchange rates from Open Exchange Rates. Fathom uses an inter-bank (without retail fluctuations), mid-market (average of buy/sell rates), rate which is calculated end-of-day using an average of rates from the preceding day.
For monthly data, Fathom uses the average exchange rate over the month to translate the Profit & Loss accounts and the month end exchange rate for translating Balance Sheet accounts.
At this stage it is not possible to provide your own exchange rates to override the rates that Fathom sources.
Where can I see the exchange rates?
To see the exchange rates used in the consolidation we recommend downloading a monthly 'Multi-Currency consolidated financial results' report from the report center:
The exchange rates for each company for the selected month are provided at the top of the Excel spreadsheet. To retrieve the exchange rates for an entire year, you will need to download the report for each month individually.
Please note that the quarterly and annual excel reports do not contain exchange rates, because the rates being applied are monthly rates, and they are applied prior to aggregation to quarters or years.