This chapter emphasizes two things: the student must try to understand why a time series fluctuates in the way it does and he can apply some tools which will organize his knowledge. The study of the problems of seasonal pattern and trend in the case of fruit and vegetable prices is intended to show the sort of investigation which must be made before more sophisticated tools are used to decompose a time series. If the seasonal pattern is seen to be sufficiently regular, the moving average may be calculated to obtain a precise measure of the trend. The principle of smoothing can be best seen in the case of a series with no trend but containing a regular seasonal pattern. The successful smoothing of a time series depends upon two things: the regularity of the pattern of fluctuations, and the choice of the number of values to be averaged.