Currency
A rate is how many units of the second currency one unit of the first buys. There is no divisor flag to get backwards. Rates are effective-dated, and a document converts at the rate in force on its own date — a rate published tomorrow never reprices an invoice raised today.
Currencies
None yet. Until there is one, every currency code on every order and invoice is free text nothing checks.
Rate types
One rate per pair per day is not enough. AP posts at the daily rate, month-end revaluation uses the closing rate, and a budget is held at a rate fixed for the year. A document with no type named uses the default — and if there is no default, DSS4 refuses rather than picking one, because “the only type there is” silently changes meaning the day a second one is added.
Rates
No rates yet
Any conversion between two different currencies will be refused until there is one. DSS4 will not assume a rate, because assuming 1 posts a foreign amount as if it were already converted.
Check a conversion
Not a calculator — an explanation. It says whether the rate was typed directly, taken as the reciprocal of the opposite pair, or worked out through the base currency, and which day it came from.