On reuters I charted the spread between the 10yr US bond and the 10yr UK bond. It gives the me the option of choosing the currency. For just the standard spread(ie: yield(US)-yield(UK)) you select none for currency option. You can also choose to display the spread in terms of pound. This changes the way the spread looks slightly and gives completely different values. I asked reuters support and they said that when you change the currency it performs a cross currency basis swap to the selected currency. Can anyone give any insight into what is going on here?