Hi David,
I don't believe there is any way to do this without some back-end modeling. Since you are using dashboards you will need to get into some query manipulation using Data Modules or FM (you didn't mention what the dashboard was sourced from). The easiest way is to take an exact copy of the query used to build the line chart you have, and just replace the query column that lists each "bucket" with a text string "Total". You can then UNION these queries and you will get each "bucket" plus all of them combined in "total".
If there is an easier way to do this, I would love to hear it but this is how I always had to achieve this.
-Todd
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Todd Schuman
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