Hello, I am testing my new system and I was wondering how TWS papertrading account simulate fills. I read somewhere on the website that it was simulated "with the top of the book". Does it mean that your buy limit order has to be touched by the real time ask to be filled? I was thinking they were using prints , like if the last real time print is one tick under your buy limit order then you get it... I f someone knows how they are simulated? Thanks a lot.