I would like to calculate the standard deviation of forecast vs. actual for
10 periods

Right now, I have to do step of step, (1) calculate deviation
(actual-forecast) (2) square deviation (3) average of the squares of the
deviation (4) square root of (3). I am looking for a Excel formular to
calcuate this...

I only found STDEV(number1,number2,...), a measure of how widely values are
dispersed from the average value. not the variation between forecast and
actual.

Please help !