Adding multiple numeric fields in a expanding table

Hi Alll,

I have created a table where the user can add multiple rows. One column of this table contains numeric fields. At the bottom of this column I have a numeric field where I want to auto sum the rows above.

I have managed to achieve this in a table with fixed rows however I cant seem to do the same in the table where the end user can add rows. Please can someone inform me if there is any javascript available to avhieve this.

Many thanks in advance

Lee