I'd like to quote the spread (i.e. price difference) between gold and silver. How an I do that? If I type anything about spreads into google I get information regarding the bid/ask spreads.
If by plot you mean to chart it, you need to use a chart provider that allows you to create a custom instrument or chart a custom spread definition. Examples are eSignal, CQG, Investor RT, Sierra Chart etc etc.
this simple indicator plot difference between two instruments, make sure you use correct symbol names. Let me know if you need something more sophisticated.
