Cumulative Computers logged on

OK, now to try explain what I am trying to do ...

I have to report monthly on patch compliance for my organisation, we have 2500 desktop/laptops and I am constantly quizzed why we don't have 100% compliance across the organisation and I have tried a million times to explain that 1400 of the machines are laptops and over the course of a month any one of these machines can be disconnected from the network for 2-3 weeks or even longer which means trying to catch them in a 4 week period (depending on where in our 4 week rolling cycle and when reports are run) can be difficult. Add to this machines being replaced / lost / broken in 60 days you still don't see all 100% of machines but after 60 days we have sccm clean out this old data.

In powerbi I have a dashboard that shows our compliance very well but what I want to have is a chart showing the number of machines that have logged on today (normally 75% of the total machines) BUT i want to show the cumulative number of UNIQUE machines that have logged on going back 60 days - this should in theory manage to catch all the machines with each day adding more machines. Each day will have all previously logged on machines + the new machines for that day counting backwards to 60 days ago.

I have the data captured live from our SCCM environment for logon on times.

In PowerBi - the table with the logon info in is called

"Clientinfo"

and column is called

"Last_Logon_Timestamp0"

format is (UK Date format)

"30/10/2018 09:06:13"

I have the data exported into excel and have worked out the query to get what I want - I have created some fake data to demonstrate. The data is plotted on a line graph to show the number of computers logged on increasing as you go back x days.

What I am struggling with is translating this into PowerBi - any help would be greatly recieved + this may be useful to any others having the same issue with trying to explain there compliance numbers etc.

 Excel - column E - "Decimal"

=COUNTIF($B$2:$B$60,">"&TODAY()-C2)/COUNTA($B$2:$B$60)

I have put 60 machines and gone back the 60 days but in reality there are 2500 machines.

Data

 graph - at top of page - graph is of columns C & D

I'm very new to PowerBi and am having issues working out how to do this on the fly (the data is refreshed from SCCM every couple of hours).