how to sum the previus 12 months with set analysis

[#1]

Hello everyone!

I’m having troubles with the following set analysis issue:

I have a pivot table with "hours per day" and i want to sum in each row the 12 previous months using set analysis (and without using de "Previous", or "above" functions) because after that I will need to calculate the variation between the value of this new column.

FECHACIERRE_CPI_QV	hs	SUM
20/01/2009	7.363	137.777
20/02/2009	11.116	148.893
20/03/2009	13.306	162.069
20/04/2009	22.964	155.566
20/05/2009	13.155	160.449
20/06/2009	11.789	160.912
20/07/2009	1.529	153.779
20/08/2009	15.765	156.168
20/09/2009	5.038	150.296
20/10/2009	10.043	148.238
20/11/2009	14.683	137.976
20/12/2009	3.138	129.889
20/01/2010	4.182	126.707
20/02/2010	6.636	122.227
20/03/2010	10.313	119.234
20/04/2010	11.004	107.274
20/05/2010	6.869	100.988
20/06/2010	7.519	96.718
20/07/2010	19.356	114.545
20/08/2010	8.261	107.041
20/09/2010	4.984	106.987

I've tried with

  SUM

({1<  FECHACIERRE_CPI_QV

= {'>=$(=Date(FECHACIERRE_CPI_QV

-365))<=$(=Date(FECHACIERRE_CPI_QV

))'} >}      
HS

)

but didn't work... any suggestion?

Thanks!!