http://s0.wp.com/latex.php?latex=MAPE+%3D+%5Cfrac%7B1%7D%7Bn%7D+%5Csum_%7Bi%3D1%7D%5E%7Bn%7D+%7C%5Cfrac%7By_i+-+%5Chat%7By%7D_i%7D%7By_i%7D%7C&bg=ffffff&fg=000000&s=3