currency conversion

I need to convert between system currency, US dollars and euros.

Problem 1 is finding out what the system currency is.

Problem 2 is the conversion. The sbobob.getcurrencyrate() functions looks ideal for this, but has problems. If a currency rate has no entry on the exacte day, the function fails. I would like to get the best estimation anyway.

When I know what the system currency is, I can do the math myself using the ORTT table, but I'm probably not the first who encounters this problem. Does someone already have a solution?