function XSTDEV, Array, Mean ; on_error,2 ;return to caller if error n = n_elements(array) ;# of points. if n le 1 then message, 'Number of data points must be > 1' ; ;; mean = total(array)/n ;yes. ;; return,sqrt(total((array-mean)^2)/(n-1)) xx = indgen(n_elements(array)) mean = total((xx+1)*array)/total(array)-1 sd = total(abs(xx-mean)*array)/total(array) return,sd end