graph based on long-term statistics, but value displayed as calculation from 2 separate measures

[gilder0]

I'm trying to show calculated COP ratio of my Heat Pump.

COP = Energy Produced / Energy Consumed.

I've prepared sensor to store values using Utility_meter and restart every hour separetly Energy Produced and Energy Consumed.

This works great when I look at current hour, but I also would like to see history values, which are stored in long-term statistics.

How can I achieve that ?