that works.
maybe you can take a look here:
http://www.mrexcel.com/forum/showthread.php?t=566959
this is what i am working on.
and using the 'Flash' report:
=IF(ISNA(VLOOKUP($A2&"*",'[Flash Report FY11.xlsx]report'!$F$4:$HZ$500,151,FALSE)),"NA",IF(VLOOKUP($A2&"*",'[Flash Report FY11.xlsx]report'!$F$ 4:$HZ$500,151,FALSE)=0,L2,VLOOKUP($A2&"*",'[Flash Report FY11.xlsx]report'!$F$4:$HZ$500,151,FALSE)))
of course the value '151' needs to be replaced with something but that is 13 columns over from the start of the June data. and the final VLOOKUP would subtract June from May which is 4 columns to the left of June.
much obliged.