Conditional sum

Hi Martin, patphilly
This is something i recently came across (in another forum)
the "range" dimensions ($B$1:$B$5 in the example) actually determine the "sum_range "dimensions while the first cell reference of the "sum_range" ($A$1 in the example) determines the upperleft startingpoint of the "sum_range".
e.g. if we write the formula as : =sumif($B$1:$B$5,"<="&B1,$A$1) or
=sumif($B$1:$B$5,"<="&B1,$A$1:$A$5) or
=sumif($B$1:$B$5,"<="&B1,$A$1:$A$2) the result should be the same.
If i understood correctly.... big if!
As for the results not updating if you change A2 to 310: this does work for me.