The CAS allows orders to be entered into the trading system for a single price auction which consists of a reference price fixing period, an order input period, a no cancellation period and a random closing period as follows:

*Eves of Christmas, New Year and Lunar New Year

• Reference Price Fixing Period (16:00-16:01)

A reference price, which sets the allowable price limit of the CAS (±5 per cent from the reference price), is calculated for each CAS security. The reference price is determined by taking the median of 5 nominal prices in the last minute of the Continuous Trading Session (CTS) and the system will take 5 snapshots on the nominal prices at 15-second interval starting from15:59:00. After determination of reference prices, the HKEX will disseminate the reference prices and price limits to the market. Orders outstanding at the end of the preceding CTS will be automatically carried forward to the CAS and treated as at-auction limit orders except that the system will cancel those aggressive orders with prices outside the permissible price limit (i.e. buy orders with prices higher than the upper price limit and sell orders with prices lower than the lower limit). For non CAS securities, reference prices are also determined in the same way as CAS securities and such prices will be disseminated to market for information as the reference price will be same as the closing price of the respective non CAS security. However, orders cannot be entered and executed on non CAS securities during the CAS. All order messaging from investors including new input, amendment and cancellation will be rejected by HKEX during the Reference Price Fixing Period.

• Order Input Period (16:01-16:06)

At-auction orders and at-auction limit orders within the ±5 per cent price limit can be entered on CAS securities. Outstanding orders can also be amended or cancelled during this period.

• No Cancellation Period (16:06-16:08)

At-auction orders and at-auction limit orders can be entered in this period. However, the prices of new at-auction limit orders must be between the lowest ask & highest bid recorded at the end of Order Input Period (i.e. recorded at 16:06), and no orders can be amended or cancelled.

• Random Closing Period (16:08-16:10)

The order rules from the No Cancellation period apply and the market closes randomly within two minutes.

• Order Matching

After the random closing period, orders for all CAS securities are matched at the final Indicative Equilibrium Price (IEP). In cases where final IEP cannot be established during the CAS, the reference price will be treated as the final IEP for order matching and will become the closing price of the CAS security. Order matching is based on order type, price and then time priority.