The peak in the ten-year moving-average curve in 1886 was caused by the number of years included in the moving average not being a true representation of the length of one full cycle. The length of the cycle changes from time to time, so that no one selected cycle length is satisfactory for the whole curve. The heavy curve sketched in by hand is the fairest approximation to show the trend of the fluctuating curve as a whole.

In Fig. 91 the points on any smoothed curve are plotted midway horizontally in the range of years included in each moving average. It is on this account that the smoothed curves, though all plotted from the same data, do not seem to end at the same year at the righthand side of the chart. Though it is good practice to plot smoothed curves in this manner with each point midway in the horizontal range of the points included in any moving average, there are times when it is not desirable to have the point on the moving-average curve fall behind the latest point on the data curve. For operating records in industrial work, the moving-average curve is convenient to show an average for the preceding twelve months or for any other length of time immediately preceding. With such curves it is usually best to have the last point of the moving-average curve plotted on the same vertical co-ordinate line as the last point of the data curve.