Trendlines can be used to show the relationship between x and y values on a chart. A trendline will run through data points, in such a way that the values above and below the line will more or less cancel each other out. Six different types of trendlines can be added to Excel charts.
6. Moving Average.
To add a trendline select the specific data series you're working with. On the PivotChart Tools menu, select the Design submenu, and on the left pick 'Add Chart Element . . . Trendline'.
A linear trendline will be a straight line that is based on the average variation between the dependent (y axis) and independent (x axis) factors.
Selecting 'More Trendline Options' will bring up a pane on the right that will allow you to select between all six options. The exponential trendline will rise or fall at an increasingly higher rate.
A logarithmic trendline is used to show values that rise or fall at first, then level off. It's the opposite of an exponential trendline.
A power trendline will curve steadily in one direction.
A polynomial trendline is based on an equation. These trendlines are used when the overall trend does not go in one direction. The higher the option number set for a polynomial trendline on the right, the more it will curve in a serpentine fashion.
A moving average trendline will smooth a trendline by basing it on the average of a specified number of periods. In this example, the period for a moving average can be set to between 2 and 19, since the chart tracks sales in 20 different weeks.