Because I can never remember them.

Level 1 halt (7% drop)

• Trading will halt for 15 minutes if drop occurs before 3:25 p.m.
• At or after 3:25 p.m.—trading shall continue, unless there is a Level 3 halt.

Level 2 halt (13% drop)

• Trading will halt for 15 minutes if drop occurs before 3:25 p.m.
• At or after 3:25 p.m.—trading shall continue, unless there is a Level 3 halt.

Level 3 halt (20% drop)

• At any time during the trading day—trading shall halt for the remainder of the trading day.