Hi, I need to calculate the difference between two values over time (once every hour, on the hour) of an input/feed that contains a cumulative m3 read from my gas meter, and store that value. So basically I need the inverse of the “Power to kWh” process. Is there something like this in EmonCMS available, or how would I go about doing that?
I had a feeling that there was a pulse rate to power, but I could easily be wrong - and which emonCMS are you referring to, the “SD” card version or emoncms.org?
If you can’t find it, and you’re using the local emoncms, then I think you need something like a script that is run as a cron job to get the appropriate values using the API call, and use those to find the average rate of change over the period of the kWh value.
Don’t ask me any more - I’m not an expert on emonCMS. 
I’ve had a similar challenge trying to get the daily honey gain from my hive weight data. It can be done using schedules and if statements, i.e. logging a start and an end value at the time intervals defined by your schedule and subtracting.
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