# how does the MA lib determine the levels for what is significant or not for ACF

I am going thru this stats course https://onlinecourses.science.psu.edu/stat510/node/48

I can follow all the steps, but have question how the lib figures out what is significant for ACF. See "ACF for Simulated Sample Data", the graph has two blue lines just inside of 0.2 and -0.2. What is the theory for determining these two levels?

significance_level <- qnorm((1 + 0.95)/2)/sqrt(sum(!is.na(indata)))