sales forecasting is an important factor for the manager in order to keep the
shop in surplus. He/she manages the shop by increasing/decreasing the
employee/part-timer on the forecasting result. In this paper, we propose a new
method to improve forecasting accuracy and confirm them by the Café shop sales
data. Focusing that the equation of exponential smoothing method(ESM) is
equivalent to (1,1) order ARMA model equation, a new method of estimation of
smoothing constant in exponential smoothing method is proposed before by us
which satisfies minimum variance of forecasting error. Generally, smoothing
constant is selected arbitrarily. But in this paper, we utilize above stated
theoretical solution. Firstly, we make estimation of ARMA model parameter and
then estimate smoothing constants. Thus theoretical solution is derived in a
simple way and it may be utilized in various fields. Combining the trend
removing method with this method, we aim to improve forecasting accuracy.
Furthermore, “a day of the week index” is newly introduced for the daily data
and we have obtained good result. The effectiveness of this method should be
examined in various cases.