Open the Select period window and check Compare with previous period at the bottom, before you click Update. The system automatically calculates a previous period of the same length: if you're viewing the last 7 days, it compares with the 7 days immediately before. With comparison on, the table cells show a percentage change next to each metric, indicating whether it went up or down versus the previous period. Your preference is saved, so comparison stays on in future visits until you uncheck it.