Here's how the New York Stock Exchange is preparing for Friday's chaotic market open

It’s going to be a nail-biting Friday.

Global stock markets are tumbling pre-market following Britain’s unprecedented vote to leave the European Union. Near 8:54 a.m. ET, Dow futures were off 495 points (2.77%), while S&P 500 futures were off 71 points (3.37%).

Rich Barry, floor governor at the New York Stock Exchange, sent out an early note on how trading could shape up on Friday.

Just a quick informational heads-up to the readership in light of the historic vote last night.

We are not saying that the following will occur in reaction, but we wanted you to be aware, just in case.

(Keep in mind, the Dow is up 500 points over the past week, and currently, the Dow futures are down 500 points — for some perspective.)

Following the referendum vote in the UK last night, pre-market trading is orderly but heavier than usual. We are prepared for the market opening with all systems operating normally.

For your information, we are providing some information regarding the use of market wide circuit breakers:

Market-wide circuit breakers provide for cross-market trading halts during a severe market decline as measured by a single-day decrease in the S&P 500 Index. A cross-market trading halt can be triggered at three circuit breaker thresholds — 7% (Level 1), 13% (Level 2), and 20% (Level 3). These triggers are set by the markets at point levels that are calculated daily based on the prior day’s closing price of the S&P 500 Index.

Market Wide Circuit Breakers are in effect from 9:30 a.m. until 4:00 p.m.

If a Level 1 or a Level 2 market decline occurs after 9:30 a.m. and up to 35 minutes before closing time (3:25 p.m. or in the case of an early close 12:25), the Exchange shall halt trading for 15 minutes. The Exchange will not halt trading if a Level 1 or a Level 2 market decline occurs after 3:25 p.m.

If a Level 3 Market Decline Occurs at any time during the trading day, the Exchange shall halt trading until the primary market opens the next trading day.

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