Old information which I guess is still correct
This how it used to be and how I think it still is but I can not confirm this as the ASX appears to have revamped their site and the old links don't work.:mad ;:
Basically the opening price is set such that the most number of shares are traded.
On the assumption that what you have displayed were the orders at opening then a price of $2.39 to $2.40 would have resulted in 10,371 shares trading:
All the buyers at $2.5, $2.42 and $2.40 would have got what they wanted;
All the sellers at $2.20, $2.36 & $2.37 would have sold all their shares and a few thousand at $2.39 would have sold.
A higher (less buying) or lower (less selling) price would have resulted in less shares being traded.
In cases such as this where several prices meet this condition then the price nearest the previous close is chosen.
All shares go through at this opening price.
Trouble is that bids can be added and pulled seconds before opening these days and thus your opening price calculation is out of date before you have finished it.
Best Wishes
Paper Tiger