mod1 <- auto.arima(x)
refit <- Arima(y, model=mod1)
> accuracy(refit)
               ME     RMSE MAE       MPE     MAPE MASE  ACF1
Training set -0.8 1.549193 1.2 -69.33333 77.33333  0.8 -0.05

ActualData FittedValue AbsolutePercentageError
120        119.5       (abs(120-119)/120)*100 = 0.83%
128        126         (abs(128-126)/128)*100 = 1.56%