On the Cross-rates tab you can set the adjustment to the currency exchange rates when they are taken from some single source (e.g. Central Bank or whatever). This is necessary in order not to loose on conversions.
The prices for products during search&book can be displayed in different currencies. And for such conversions the system will use currency exchange rates established on the day of payment plus this percentage.
For example the exchange rate is EUR 1 = USD 1.18585. With a 3% increment to the rate it will be USD 1.22142.
To set these cross-rates,
Go to the contract, tab cross-rates.
Click Edit to switch to editing mode.
Fill in required % for each currency (note that you can set different amount of adjustment for each of them).
Click Save.