Hi, i calculated the autocovariance of a vector x of length n, using result <- acf(x, lag, type="covariance") and expected, that result$acf would contain the values cov(x,x), cov(x[1:(n-1)], x[2:n]) ... However, acf does not calculate this covariances. Instead of cov(x[1:(n-i)], x[(i+1):n]) i am getting ( (x[1] - m) * (x[i+1]-m) + ... + (x[n-i]-m) * (x[n]-m) ) / n where m = mean(x). I anderstand, that for efficiency reasons only the mean of the whole vector x is substracted instead of the means of the partial vectors. But why does it divide by n instead of n-i? Christian