I connected some nodes together in this calc_average_last3_months.knwf (92.1 KB) workflow. I used a Column Appender because I assume the order of both table is the same (?). I also created a date back in time (3 months) that will be used later on to do the filtering in the DateTime Based Row Filter. Because the dates differ per row,I used a Chunk Loop to do the calculation for every in the table. Hope this give you some directions to solve your problem.