Yet another Moving annual total (MAT) question

[gbernabo]

Dear Qliksensers, I've been reading this forum looking for this answer many times to no avail. 

I need to create a bar chart with the sum of my data grouped in MATs, that is the last month I have loaded (usualy two months before the actual date) plus the previous 11 months.

I've created the autocalendar but I have no idea how to get from that to MAT, only to YTD.

My data looks like this:

Sales	Imp_date
20117	2020-Sep
7829	2020-Aug
13415	2020-Jul
14975	2020-Jun
16716	2020-May
22004	2020-Apr
5919	2020-Mar
16049	2020-Feb

And so on until 2007-Jan

And I expect to get a chart like this:

Where each Year is the sum of 12 months.

Can you give me a clue as how to work this out?

I've attached a mock data file to use as example.

Thank you in advance!