Hi Uz Agree that there's buying that is not on the screen but I...

Hi Uz
Agree that there's buying that is not on the screen but I think it's a little different - and possibly a lot more bullish - than your "surplus volume" calculation.   That bidding at 33c is what the brokers call an "Iceberg",  that automatically keeps putting up more bids until completed. It could be for only a couple more reloads or it could be for millions of shares.  I occasionally use "Icebergs".  It shows that the buyer (or seller, where applicable) does not want us to see the size of his package (so to speak).   

I suspect your screen referred to "surplus volume" at what the brokers call "the cross-over" or "the match" - i.e.. the open or close - when the opening bids were being matched against offers and a match price was calculated, at which price there was "surplus volume".  

That "surplus volume" is positive when bids exceed offers at that price, or negative when offers exceed bids at that price.  The phrase "surplus volume" disappears after the market is fully opened, I believe.

At the time of typing this, that buyer has 30,845 left on that tranche of his order at 33c.  When that is satisfied, the order will add another tranche (of whatever size the buyer has dictated), at the bottom of the queue of buyers on the ASX platform but above the queue on ChiX.  
Cheers