You place an Extractor element in the repeating group, and a Data element outside the RG. You then specify which field the Extractor is looking at for each row in Column 1, and what data type to expect in the data element Column 1 (in this case, ‘number’). You can then set the Data element’s value in your subtotal element as the Data Source, and it would be something like ‘RG Data’s Column 1 List: Sum’