Partial Accumulation in table

[#1]

I am trying to do a partial accumulation on the spend column (column 3) - I have a full years budget column(1) and want the plot spend so far against it, if I use full acculualation (column 6) I end up with a static figures for months that haven't happened yet. I tried using the above function (column 5) but ended up with strange figures. Any suggestions?

The set analysis i'm using forthe buget, spend etc. is as follows:-

     sum({$<BER_DeaTran_Period_Name=>} BER_DeaTran_Current_Budget)

Thanks in advance.

Stephen