I feel like there should be two dozen answers to this question, but I literally can't find one, at least not for the C# development environment.  If there is, I apologize in advance.  Simple question: how do I get the settlement price (not necessarily the close price) of US Index, such as SPX?  I want to know the settlement price used when the options are exercised after market close.  Since Index options are cash settled, I need to know the settlement price to calculate P/L, unless there is another way?