HOW TO CALCULATE INSTALLED BASE (MOVIL)

Hello  

I need to calculate the installed base of hardware  calculating the % to actual time but when i go backward its not working , (sory for mi bad english ) 

I can attach the file u need to convert to dax expression its made in excel and i have to do manually (for each client in each modelo in each month ) and i like to know how to automatize the process , i also try to make the expression by miself and the final month is the same  , but goin backward its not (thats because the expression i mada its not mobile across the time) 

In fine original  is the excel way made by hand every month with every client 

in the second file 

i have the file i made with the expression but if you see , only the last month is the same , (the hw installed base in jun 2018  is the same in excel way and in dax way , but may 2018 is not the same )