The Pie chart is the only chart that does not have any axis. The pie chart is used to represent each segment (element or field) of the chart as a relative portion of “the whole”. In this sense, the entirety of the pie represents 100% with all of the segments added together. This analysis not only allows each segment (by virtue of size) to be compared to the other segments but it also enables analysis of each segment in the context of 100%. For example, if there are twelve months in the year, and each month’s sales are represented by a segment (or piece) of the pie, then all of the segments taken as a whole represent 100% of the sales for the year. In this context, users can see which sales contributed to most to annual sales (bigger slice of the pie) while also seeing how much of the year is represented in each segment. This example is demonstrated in the image below where each month of sales is a different slice of the pie and all of the segments added together represent the entirety of sales for the year.
Hovering the mouse over any single element in the chart will result in the numeric value represented by that segment, along with the name of the segment appear in an on-screen help window. In the image below, we see the first month of each quarter (January, April, July and October) displayed as segments (or pieces) of the pie chart with the hover window appearing at the current cursor position in the October segment.