OH3 Rules DSL Calculation for kWh - UoM?

Setup, Configuration and Use Beginners
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1

Hi All

I have the following rule which I am trying to use to calculate my Last Months electricity consumption:

rule "EM Mains Monthly Process"
when
    Item ShellyEM_MAINS_TotalEnergy_Switch changed to ON
    //Time cron "0 10 10 * *"
then
    var EMToDate = ShellyEM_MAINS_TotalEnergy.state as Number 
    logInfo("shelly_em", "EMToDate: " + EMToDate.toString())

    var PreviousMonth = ShellyEM_Mains_TotalEnergy_PreviousMonth.state as Number 
    logInfo("shelly_em", "PreviousMonth: " + PreviousMonth.toString())

    var UsageLastMonth = (EMToDate as Number - PreviousMonth as Number) 
    logInfo("shelly_em", "UsageLastMonth: " + UsageLastMonth.toString())

    //ShellyEM_Mains_TotalEnergy_PreviousMonth.postUpdate(EMToDate)
    //ShellyEM_MAINS_TotalEnergy_Monthly.postUpdate(UsageLastMonth)
end

The log entries I see are:

09:28:59.745 [INFO ] [g.openhab.core.model.script.shelly_em] - EMToDate: 16653.434 kWh
09:28:59.745 [INFO ] [g.openhab.core.model.script.shelly_em] - PreviousMonth: 16648.39 kWh
09:28:59.745 [INFO ] [g.openhab.core.model.script.shelly_em] - UsageLastMonth: 18158400

So EMToDate and PreviousMonth are correct, however the calculated result UsageLastMonth is not.

I am currently not updating the Item so preserve my data as the calculation is not working.

I cannot work out what I have done incorrectly? Maybe something to do with UoM, but would appreciate any hints?
Items are configured as Number:Energy

Any help would be appreciated.

2

Found solution here.

3

It’s the “as Number” that caused your issue, by treating the Quantity Type values as plain Number values you lost the magic units-of-measurement handling capability.

More about this here, tips’n’tricks for Quantity types -