Basically, the first thread explains what is the correct way to achieve your goal and the second offers a workaround, which is not very reliable. Personally, I'd go with the approach in the first thread and maybe create a data source, from which I can sum the totals, which are displayed in the two text boxes. Since their values probably also come from data sources, it should be possible to combine those data sources into a single one and use it for calculating the grand total.