Well, it's not actually part of TWS (not in the menus I looked at, anyway). It's found under "report management->Stress Test" when you access your account on the web (or jump to the web from within TWS). It allows you to see how your portfolio performs for various percentage moves up & down (both overall and individual positions). Kind of a nifty little feature, but it'd be nice to have it in the platform rather than as a webtool. It certainly doesn't jump out at you. I don't access the website very often, and just happened to stumble upon it. Anyway, thought I'd share in case you hadn't been aware of it.