Show average value per year in chart

Hi team, looking for any advice on charting an average value per year for each organization (using connected to logged in user). I have the Year already extracted from the Created By field using a date equation. I could create a chart using Year as the group by field, but the only calculation available seems to be total, not average. I can create a roll-up field in a separate table, but it doesn’t seem that you can chart the roll up field (it isn’t available in either the group by or by options). If folks have any ideas, I would appreciate it. Thanks!