Difference (min/max) on hover?

Hello, new to Grafana, making my first experiences.
I do have a influxdb with PV-Battery Cellvoltages (16). Want to have a Difference shown of the highest and lowest voltage of all 16 Cellvoltages on hover with the mouse on the graph.
Would that be possible?

now all data is inside grafana, how do I calculate from highest to lowest value the difference?
transform data? query? Thx for help!

not possible, transforming and calculation possible?