Minitab generates the autocorrelation function (ACF) with 95% confidence limits for the correlations (red).

The ACF for the sales data shows a large negative significant spike at lag 1 (this means that the autocorrelation of the successive pairs of observations within 1 time period is not within sampling error of zero). All of the other autocorrelations (for lags 2 to 15) are within the 95% confidence limits. This pattern is typical to a moving average (MA) process of order one.