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.