Currency conversion, the easyJet way

I was surprised to see that easyJet does currency conversion in rather "arbitrary" way:

- for a one-way flight I wanted to book for my sister on August 31st, 2007, the website converted Swiss francs to euros as follows:

103.95 CHF = 66.68 EUR (the links show screen captures with the price in Swiss francs and in euros)

which means that the exchange rate used is 1 CHF= 0.64 EUR

- for the return flight, the price is 102.87 CHF = 62.83 EUR

so the exchange rate is 1 CHF = 0.61 EUR!

The difference is quite striking when you see that one Swiss franc in the flight prices is worth about 4 euros!! A rather expensive CHF, it seems! while the official rate of the day was in fact 0.61.

EasyJet also uses arbitrary conversions for the priority boarding (11.25 CHF = 7.5 EUR, that is, 1 CHF = 0.68 EUR, and 17 CHF = 11.5 EUR, that is, 1 CHF = 0.66 EUR), but this is somehow understandable since it's a fixed value, it is not computed in real-time as the ticket price is supposed to be. However, I am quite intrigued about the kind of converter they use for the real-time price computation and about the hidden variables it depends on...