Help with RangeSum and Above in Chart

[mikelees80]

I been asked to produce a chart that shows a cumulative count of the pieces of equipment we have installed by Month.

I have managed to do this by using the RangeSum , above and aggr functions.

Here is my code

=round(Aggr(

RangeSum(Above( sum({$<

[Instance Summary - Install Date Num]={"<=$(vtoday)"}

,[Instance -  Date Calendar Year Period]=

,[Instance - Status]-={'Not Installed','Replaced','Uninstalled','Terminated'}

,[Instance - Serial Number Flag]={'Y'}

, [Instance - Install Date Flag]={'Y'}

,[Location / Customer Type]={'Installed At'}

,[Instance - Include Flag]={'Y'}

>} [Instance Summary - Count]), 0, RowNo())), [Instance -  Date Calendar Year Period]))

It works great however the chart by default without fiters shows the first install period which is 1999 resulting in displaying 235 columns!!

What they want is to have a cumulative total by back to 1999 but only display the last 12 columns ( ie 12 months)

Current (just showing from 2014)

They want to display without filters needing to be selected ( back 12 months from today so 2017 - 10 - Oct)

Any ideas?