I usually have Fidelity running my portfolio on my phone. When I ask for a detailed quote to get the bid/ask etc. I often find it's changed from what was showing on the portfolio. I really don't know if it's a coincidence, or if one, or the other, just doesn't update as frequently. On more than one occasion I've seen the bid higher than the ask yet no trading seemed to be occurring. I tend to think that updates don't happen as quickly as we'd expect them to.
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