A graph of the difference between the two symbols

 
Hello,
I'm looking for an indicator that would show me a curve in a new window that shows the difference between the two symbols.

Do you know of any such?

(MarketInfo ("EURAUD", (MODE_BID + MODE_ASK) / 2) -MarketInfo ("EURCAD", (MODE_BID + MODE_ASK) / 2))

Thank you for your help