I steal this idea from grafana. But it is really nice to have a table with fast access to values in the legend like:
- current value
- average value for the given period of time
- max value for the given period of time
- min value for the given period of time
Screenshot from grafana (look at the table in the legend):
Link to grafana tool: https://grafana.com/
This summary table should be optional to show in the legend when you configure the visualization.