Single stock derivatives: calendar spread margin benefit not available on expiry day; exchanges must implement changes within three months. The circular removes calendar spread margin benefit for single stock derivatives on a contract's expiry day: any spread pairing a contract expiring that day with another expiry will not receive offsetting margin treatment for that pairing, while spreads involving only later expiries remain eligible. Stock exchanges and clearing corporations must update systems and amend rules to implement the change; the measure is effective three months from the circular's date.