You have to use the Before Formula Scripts
If this is used for col(A) and col(B) only, then put the following script into the Before Formula Scripts box in Col(B)'s Set Column Values dialog
sum(col(A));
col(B)[1]=sum.max;
You can then turn on Recalculate to Auto.
If you want this to be general, to calculate from previous column, then write it such that it can be applied to other columns:
sum(wcol(_ThisColNum-1));
wcol(_ThisColNum)[1]=sum.max;
To find out about the sum function in Labtalk, just google "labtalk sum" and it will land to this link
http://wiki.originlab.com/~originla/wiki/index.php?title=LabTalk:Sum_(object)
CP