Why the total numbers of by day data not equals to by month data with the segment of "last month"

[DebbyNPL]

Hi all

I'm trying to see the data of some key metrics such as "PV", "UV" and "Bounce Rate"...

But I notice that when I use the default segment of "last report month", the total by-day data was not equal to the by-month data for nearly all the metrics. 

When i look to the "Month" data, the data showed correctly. 

But when i look to the by day data, less data was show on the table. 

But when i combine two dimenssion together, the by day data showed correctly again. 

Could anyone explain to me why this happen?  It will be really helpful.

Thanks QAQ

[leocwlau · Accepted solution]

I guess that is due to the 31 days of May and compare to the 30 days of Jun.

In the first image, the dimension is Jun but the actual report number is May data since you have the Last Month segment.

In the second image, the dimension is Day so items are listed from 1-Jun to 30-Jun but the actual report numbers are 1-May to 30-May, and the 31-May is missing as there is no 31-Jun to match.