This is a EURUSD converted index. It show the value of the index at the EURUSD current ratio. The Histogram is the spread between the index and the index in Euro. So if you use Euro to buy US stock, you can check at the spread and try to enter with high level spread (this is when Euro is strong) and exit when is low (like now). This can add a bit of profit to our trade. The opposite can be used by US investitor that want to buy stocks in EURO.
