I have a cross-tab like this

                  JAN    FEB    MAR ....... DEC (the 12 months as columns)
year 2006
   item 01     150    205      300 .......    550
   item 02       80    190      284 ........   620
 
year 2007 
   item 01      458    235      224 .......... 781
   item 02      154    254      134..........  254   
 
year 2008
   item 01       245    154      544           1243 
   item 02       524    254      124 .........   924      
 
I want to know if is possible to have a formula that take the value of each month and compare with the previous and make a calcule like this...
 
                  JAN    FEB    MAR ....... DEC (the 12 months as columns)
year 2006
   item 01     150    205      300 .......    550
   item 02       80    190      284 ........   620
 
year 2007 
   item 01      458    235      224 .......... 781
                   (205)   (14)
   item 02      154    254      134..........  254   
 
year 2008
   item 01       245    154      544           1243 
   item 02       524    254      124 .........   924  
 

where (205) and (14) are calculate from:
(205) = (150 - 458) * 100 / 150 I have to make this operation for each month takin the values from item 01 from 2006 with the values from item 01 from 2007 and so on