I tried to predict time series data by following the vedio and many other topics here. The accuracy is calculated by the "% validation" and "% forecast performance". The result "predict trend accuracy" actually describe the trend accuracy, which is usful if I predict next day stock price. But if I want to predict sales for future months, then it's not enough to describe the accuracy by trend only. I'm thinking of using something like root mean squared error. I tried to replace the operator "% forecast performance" with operator "performance" but the result looks strange. Anybody knows how to do that correctly? What the average root mean squared error is calculated then? Will the " root mean squared error" been simply averaged over all iterations?