How F&O buildup and option walls are computed

All F&O analysis uses NSE's settled end-of-day F&O bhavcopy, so it never reads a half-updated chain.

Futures buildup

For each stock's near-month future, the direction of the price change and the direction of the open-interest change place it in one of four boxes: long buildup (price up, OI up), short buildup (price down, OI up), short covering (price up, OI down) and long unwinding (price down, OI down). Price moves under 0.05% count as no clear buildup. Lists are ranked by the size of the OI change. Basis is (future − spot) ÷ spot, and values beyond ±15% are ignored as data errors.

Option walls

• Call wall: the strike at or above spot with the most call open interest (within 25 strikes).
• Put wall: the strike at or below spot with the most put open interest.
• Put-call ratio: total put OI ÷ total call OI.
• Max pain: the strike where the total value of all open options at expiry would be smallest.

Walls are presented as crowded strikes, not levels the market must respect.