I look at both Google Finance and Robinhood depending on where I am, and at 8:30am, for example, the SPY premarket on Robinhood and the S&P500 futures are about the same (Google Finance is about a minute behind). But today for some reason I'm seeing about a 0.7% gap between them. I'd always assumed they would move in lockstep with each other. Is there a reason for this? Something to do with dividends maybe?