UC Trade

Can anyone explain what an uncrossing trade is .

This explanation from III board does make it a little easier to understand....

The last trade at 16:35 is a "UT" uncrossing trade and can generally be ignored. For those of you who want to know how it is calculated:

The Uncrossing Algorithm performs a series of passes within an individual market, matching the best bids and best offers present in the price time sequence.
When all crossed volume has been matched, an Uncrossing Trade Price can be determined for the market. This price is found by applying one of the following calculations.
The calculation used is determined by the presence of residual limit volume within that market following uncrossing.
The four possible cases are:
• There is no remaining bid or offer limit volume in the market Uncrossing Trade price = the average of the bid and offer price from the last match.
• There is remaining limit offer volume but no limit bid volume in the market
Uncrossing Trade Price = offer price from last match.
• There is remaining limit bid volume but no limit offer volume in the market
Uncrossing Trade Price = bid price from last match.
• There is remaining limit offer and limit bid volume.
To determine the Uncrossing Trade Price in this case:
• Determine what the Best Offer Price is. Determine what the Bid Price is from the last match. Take the lowest of these. This is known as the ‘High Price’.
• Determine what the Best Bid Price is. Determine what the Offer Price is from the last match. Take the highest of these. This is known as the ‘Low Price’.
The Uncrossing Trade Price is the average of the ‘High Price’ and ‘Low Price’. If this value is halfway between two tick values the price allocated to all uncrossed business will be rounded towards zero (rounded down if the value is positive, rounded up if the value is negative).
If no matches occur within a market there will be no Uncrossed Trade Price for that market.