Imagine the site that has one very strong trade and the rest of the trades are so-so. According to the priority this site will always be on the top position, whereas the rest of the sites will get the second, third and other positions. This trade will get almost all hits. To avoid this situation out settings exist. We take for example first 10 traders in the line to get a hit and we give a hit to one of this 10 at random. But to follow the priority ( the trader which is higher in the list is more likely to get a hit than a trader placed lower in this list) we set as chance to get a hit for each of position. For example, trader at the first place gets 50% change to get a hit, second place - 30%, third - 10 and so on.