Imgur Image containing screenshot of question. The "Current Market Value" price is often different from the "Last" price. What's the difference in meaning between the two values? I did a couple searches on Google, in ThinkorSwim's documentation, and on Investopedia, but found nothing that answered the question. Investopedia compares market value to "book value", which I don't think is the same issue. In the ToS documentation, I found: However, in my experience, the Mark is generally not the Last price. In fact, the Mark price is generally a few cents from the Last price. As we speak, 9/13 at 1 PM EST, the Mark price is 794.25 and the Last price is 796.00. ToS talks about the Mark price being the average of the bid and ask prices when dealing with Options. Even though I am not trading Options, I checked the Bid/Ask prices and the Mark price is not the average of the two. Is it possible that it is the average of ALL the Bid/Ask prices, as seen in the Level II figures? As they constantly change, I took a screenshot and averaged the prices based on number of contracts and also without respect to the number of contracts. The Market Price is definitely not the average of the Bids/Asks, at least not for futures. What do you guys think?