During the 1987 global stock-market crash, which U.S. index lost 22.6% on Black Monday?

The Dow Jones Industrial Average lost 22.6% during the 1987 global stock-market crash's Black Monday session.

Black Monday occurred on October 19, 1987, and the Dow's one-day percentage decline remains the largest in its history. The fall was part of a worldwide rout that affected markets in Hong Kong, Europe, Australia, and elsewhere before reaching the United States.

Several factors were associated with the crash, including elevated valuations, concerns about economic conditions, international currency tensions, and computerized portfolio-insurance selling. No single cause completely explains the event.

The percentage loss is different from the Dow's later record point losses, which became larger as the index itself rose. This question concerns the percentage fall, not the number of index points lost.