Directional exposure added or removed overnight, from the change in open interest weighted by delta. Open interest is what somebody was willing to carry — volume counts everything opened and closed inside the session. This is not order-flow sentiment: signing a trade buy or sell needs a per-print tape with trade-time quotes, which we do not receive, and a closing-print classifier would mark almost the entire market "sold".

Δ added sums each contract’s overnight change in open interest multiplied by its delta and by 100, so it is in shares of delta. % of OI divides that by the same book measured in shares, which is how much of the existing position the day moved. Put deltas are negative, so opening puts subtracts and closing them adds — the sign is the direction of exposure, not the direction of trading. Gamma is shown gross, calls and puts separately, rather than as a single net dealer-gamma line: netting requires assuming which side of every open contract the market maker holds, and that assumption is not in our data. Where gamma is concentrated is observable and is where hedging flow gathers; who is short it is not.