Answer: The answer lies in Frequency differentials. If a site has a high daily frequency (browsers visit the site often within the space of 1 day) then that site will have high daily UB figure. However, when it comes to calculating monthly UBs the monthly figure is de duplicated so all those that came back multiple times on one day will be counted only once during the month. It is for this reason that sites with lower average daily UBs can in fact rank higher than those with higher daily average UBs in monthly reports.