For expositional purposes the following order book scenario will be adopted and the new and old algorithm applied to determine the call auction price:

Order book for stock X at the conclusion of the pre-open period

Broker	Quantity	Bid	Ask	Quantity	Broker
199	500	640	610	1000	606
227	500	639	640	500	317
298	500	639	641	520	150
288	1000	634	642	550	203
144	500	633	643	519	202

Old algorithm - a weighted average price is calculated from the last two remaining orders that are matched. This price is based on the following formula:

((buy quantity x buy price) + (sell quantity x sell price))/(buy quantity + sell quantity)

The last two orders matched in this example consist of a buy order for stock X at $6.39 (broker 227), with an available quantity of 500 shares and a sell order for stock X at $6.10 (broker 606) with an available quantity of 500 shares. This gives an auction price of [((500 x $6.39) + (500 x $6.10))/(500 + 500))] = $6.245. This price is applied to all trades in the auction.

New algorithm - to facilitate the application of the new algorithm it is useful to reconfigure the example order book by sorting all prices from highest to lowest. This is presented below. The algorithm is applied as follows:

Principle 1. Determine maximum tradeable volume. As is evident from the above Table, maximum tradeable volume occurs at prices between $6.10 and $6.39. As there is more than one price that exhibits maximum tradeable volume of 1,000 shares, we must progress to Principle 2.

Principle 2. Determine the minimum surplus within the price range, $6.10 to $6.39, as established in Principle 1. Minimum surplus occurs at 500 shares at each price from $6.35 to $6.39. As there is more than one price with minimum surplus, progress to Principle 3.

Principle 3. Determine the market pressure. In this case the surplus of 500 shares is buy surplus at each price. Buy pressure is denoted by a + sign. In this case, as only buy pressure exists, the auction price is the highest price in the range of $6.35 to $6.39. Therefore the auction price is $6.39.

Under the new and old algorithm the same volume of trades execute and the best bid and ask remains the same. Brokers 199 and 227 buy 500 shares each at the opening price and broker 610 sells 1,000 shares at the opening price. The best bid and ask is left at $6.39, $6.40. However, under the old algorithm all trades execute at $6.245, while under the new one all trades execute at $6.39. Therefore, the new algorithm has allowed the price to adjust upwards to reflect supply and demand.