Charting item aggregate value or Sum by day

Is it possible to chart by an aggregate value .
eg If I write hourly can I sum for a daily chart?

There are not a lot of details to go on here, but in general create a separate Item to store the daily sum. At midnight (or there about) trigger a rule to calculate the daily total and update the daily sum Item.

Clarification, I’m persisting a item every hour, however I’d like to chart by day but sum the values.
ie I’m logging kwh every hour and would like see daily totals over the month.

Same answer. If you want to chart by day, you gotta save the data by day in a different Item (or change your existing Item to only save once per day).