Distinct count in chart

I need to create a barchart of the number of visitors to our facility over the years. Each record in our table is is one day, so if someone was here more than one day there are multiple records. I have created a summary report using the distinct count feature and then group by Year, but can't figure out a way to do it with a barchart.

Is there a formula I can use to count the number of unique visitors? Or can I create a barchart using the summary report?

Thank you,

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Rob Brown
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