By "leading counts" do you mean that you have a summary field that provides these counts--one subtotal for each sorted group of records?
If you can't make the following general description work for you, please use Post a new Answer to tell me what version of FIleMaker you are using as the interface for setting up a chart is different in each version.
Refer to the summary field as your Y series data. Specify "Summarized data", "sorted groups" as the data source option for your chart. Then be sure to use a find and a sort to pull together the records that you want to chart, sorted into the groups that you want to represent each wedge of the pie chart.
(It may help to think of each "wedge" of the chart as a special kind of sub summary layout part if you are familiar with how that layout part is used in a report.)
I forgot to mention, I am using FM12.
Specify the summary field in "Slice Data". Then click Data Source and select "Current Found Se"t from the Slice Data drop down and also select the radio button for "Summarized groups of records".
We used a leading grand summary. Whenever I try to make a chart from the 9 counts, I get every entry charted instead of the 9 counts.
You have to sort your records to group them by whatever field stores the value that identifies each "wedge" in your chart.