[Minitab] - What function is used for autocorrelation confidence bands

I'm just curious as to what function minitab uses to calculate 95% confidence bands for the autocorrelation function (see red dashed lines in attached picture).

I am familiar with the asymptotic standard error of 1/sqrt(N), where N is the sample size, but that is constant and not what is being used here. I've done some research and found different methods for computing these bands, but I can't replicate Minitab's output with any of them.

Help would be greatly appreciated on this matter. Thanks!

- Matt