Which currency a price is in, what you are actually charged, and what your account setting changes.
Every price on Artmire is shown in the currency the seller listed it in. Nothing is converted for display, so what you see on an item card, on its page and at checkout is the same figure in the same currency throughout.
You pay in the item's currency. If that is not your own, your bank or card provider converts it at their rate when the payment goes through.
This is why a card statement may not match the total on screen to the penny. The difference is your bank's exchange rate and any fee they add — it is not a different price, and Artmire never sees it.
Preferred Currency on your account page — EUR (Euro) or USD (US Dollar) — is the currency your account credit is held in. It does not change the prices you are shown and it does not change what you are charged for an item.
Changing it converts your existing balance into the new currency there and then, so the money is not lost, only restated.
Checkout works out what your balance is worth against the item's price and shows you what the credit covers and what is left to pay.
That calculation uses Artmire's own conversion rate, not a live market rate, so it can differ slightly from what your bank would have charged. It is applied consistently in both directions, and the figures at checkout are what you are held to.
Every shop is independent and each seller prices in the currency they work in. Two items in your cart can therefore carry different currencies — which is exactly why the cart groups by seller and by currency, and asks you to pay each group separately.