Here is a bug I see in client code at least once a month:

# DO NOT do this gex_now = api . get ( " /v1/flow/summary/SPY " )[ " live_gex " ] gex_open = api . get ( " /v1/exposure/gex/SPY " )[ " net_gex " ] intraday_move = gex_now - gex_open # ❌ meaningless

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net_gex and live_gex look interchangeable. They are not. They come from two different surfaces of the API, computed against two different open interest numbers, answering two different questions. Subtracting one from the other gives you a quantity that means nothing — not "intraday gamma move", not "change since open", just noise. This post is the canonical explainer of where each number comes from and how to keep them apart.

Two questions, two numbers

Dealer-positioning analytics has exactly one input that matters: how many contracts are open at each strike, and on which side dealers sit.…