user measure google analytics

I thing this is correct. When you use different time periods from the GA then you will see the "unique" users for the each selected period. Eq. when monthly view then it matches with monthly view in GA page. 

In my opinion, the easiest way to get correct numbers for different periods is to extract separate tables. Daily unique then take the stats by days. But you cannot sum those days, because monthly stats is different then. Its all about how to explain the result then.