The graphs for the autocorrelation function (ACF) of the ARIMA residuals include lines that represent the significance limits. Values that extend beyond the significance limits are statistically significant at approximately α = 0.05, and show evidence that the autocorrelation does not equal zero.
| k || lag; k = 1, 2,... |
| xt ||value of x at row t |
| ||mean of x |
| n ||number of observations in the series|