Table 4-4 shows the weekly rentals data for the Movie Video Store along with the results of using a three-week moving average to forecast future sales. Examination of the error column in Table 4-4 shows that every entry is positive, signifying that the forecasts do not catch up to the trend. The three-week moving average and the double moving average for these data are shown in Figure 4-6 . Note how the three-week moving averages lag behind the actual values for comparable periods. This illustrates what happens when the moving average technique is used with trending data. Note also that the double moving averages lag behind the first set about as much as the first set lags behind the actual values. The difference between the two sets of moving averages is added to the three-week moving average to forecast the actual values