Lag function in DAX

Greg_Deckler Thanks for coming back so quick.

So looking at the article you sent it adds a calculated column into the physical dataset as per the below screenshot?

Is there a way to do it just where I can create that column inside my below DAX query? As what I am looking for is quite bespoke to a single report and don't want it going into the general dataset.

Apologies if I have missed the point here - DAX confuses the life out of me!

Greg_Deckler Actually I got it working with the below from your article. I removed the "Prev Decline" column from inside the summarize and then added wrapped it in a ADDCOLUMNS further down which did the trick.

Thanks a lot for the help! 

Hello Greg_Deckler LukeB,

My 1st column has a list of Equipment, and the 2nd column has the date/time they failed in the date/time format. For each of these equipment, I am trying to find the difference between date/time they failed (difference between rows) and calculate their summation at the end.

I created the Index column and wrote the following DAX code to solve this issue:

DIFF =

var _lasttime = CALCULATE(MAX('Sampling'[BreakDownDate]),FILTER('Sampling','Sampling'[Index]=EARLIER('Sampling'[Index])-1))

return

DATEDIFF(_lasttime,'Sampling'[BreakDownDate],MINUTE)

It is giving me the right number if I just select(filter) just 1 equipment but as I keep adding Equipments to the table it gives me wrong summation of Breakdown date towards the end. As a whole on 2000+ different equipments, my numbers are not that far. But individually for those equipments my numbers are sharply and significantly different for many equipments. 

Can you please suggest a better DAX code than above to resolve this issue further?