Every published gamma-exposure construction — including the one Cboe's own research uses — prices gamma the same way: Black-Scholes, one implied vol per contract, inverted from the quote mid. The literature offers upgrades: fit an arbitrage-free smile (SVI), or replace the lognormal with a Gram-Charlier expansion whose skew and kurtosis supposedly matter most at 0DTE. No paper measures what switching the model does to the number a terminal actually ships. So we did: the production machinery runs verbatim — same book, same dealer weights, same root finder — with only the vol input swapped, over 14 sessions including the two worst flip days in our archive.
What moves:
swap
zero-gamma flip (median)
net gamma at spot
