help里有写The algorithm returns an estimator of the generative distribution's standard deviation under the assumption that each entry of itr is an IID drawn from that generative distribution.
差1什么的应该说的是If corrected is true, then the sum is scaled with n-1, whereas the sum is scaled with n if corrected is false with n the number of elements in itr.
julia> itr=[1,2,2,3,3,3,4,4,5]
...
julia> sqrt(sum((itr .- mean(itr)).^2) / (length(itr) - 1))
1.224744871391589
julia> std(itr)
1.224744871391589
julia> sqrt(sum((itr .- mean(itr)).^2) / length(itr))
1.1547005383792515
julia> std(itr,corrected=false)
1.1547005383792515