Not used this on holiday in real life situations, but on trial it does appear to do the job admirably, once you have converted the exchange rate to its reciprocal : for example, if the exchange rate for the US $ is 1.3 to the £; then you need to divide 1 by 1.3 = 0.7692.
This is the amount to put in as the " set rate " and away you go. The calculator will retain that rate until you put in another one, so you then don't have to put in a rate every time you use it, for the duration of the holiday.
Whilst it is advertised as a Euro converter, it can be used for all currencies.