You can change the way that values are calculated in a chart. For example, you may want to display average sales instead of total sales. You can apply data calculations to the values represented by one or more chart element. Different chart elements represent different types of values. For example, one bar can represent sums and another bar can represent averages.
Chart item totals added to your report are aggregates (literally, totals of totals), and can be recalculated using a Dashboard. When applied to totals, data functions can either apply the calculation to the "surface" or "underlying values".
When applied to surface values, data functions recalculate the values in the visible cells or "surface" of the Chart. When applied to underlying values, data functions return to the unaggregated values beneath the Chart and recalculate based on those values. When "underlying values" are used, the results often are shown incongruous with the aggregate "surface" values of the chart element. In other words, a total of the underlying values does not match the total of the surface figures.
To match surface-level Chart values in your calculation, you can instead use "surface" total functions. For example, if you apply a surface average to a total, the total is converted to the average of the surface values in the corresponding element.
To apply a data function: