Calculation I can't explain

Setup, Configuration and Use Beginners
1

Because I saw a strange value of a item I added some logging. See below the logging I create every 30 sec.

2022-01-30 23:52:00.213 [INFO ] [nhab.core.model.script.default.rules] - Waarde vastleggen: 7.871 kWh 50.737 kWh 0 kWh 10.274 kWh 5.925 kWh
2022-01-30 23:52:30.215 [INFO ] [nhab.core.model.script.default.rules] - Waarde vastleggen: 7.881 kWh 50.737 kWh 0 kWh 10.274 kWh 5.935 kWh
2022-01-30 23:53:00.211 [INFO ] [nhab.core.model.script.default.rules] - Waarde vastleggen: 7.881 kWh 50.737 kWh 0 kWh 10.274 kWh 5.935 kWh
2022-01-30 23:53:30.232 [INFO ] [nhab.core.model.script.default.rules] - Waarde vastleggen: -4.329 kWh 50.737 kWh 0 kWh 10.274 kWh 5.945 kWh
2022-01-30 23:54:00.214 [INFO ] [nhab.core.model.script.default.rules] - Waarde vastleggen: -4.329 kWh 50.737 kWh 0 kWh 10.274 kWh 5.945 kWh
2022-01-30 23:54:30.215 [INFO ] [nhab.core.model.script.default.rules] - Waarde vastleggen: -4.321 kWh 50.737 kWh 0 kWh 10.274 kWh 5.953 kWh
2

It is all about the first item logged when it changed from 7.881 kWh to -4.329 kWh
The calculation is below. The value in the log files are between {}

ElectraAbsoluutPerWeek.state {7.881 kWh}  = SMAAbsoluutPerDag.getStateAs(QuantityType) + ElectraAbsoluutPerWeekReference.getStateAs(QuantityType) {0 kWh} -
                                 ElectraLeveringPerWeek.getStateAs(QuantityType) {10.274 kWh} +  ElectraVerbruikPerWeek.getStateAs(QuantityType) {5.925 kWh}

SMAAbsoluutPerDag.state not logged but must be >= 0 kWh and can’t have changed during the evening.
What can be the issue?

2

What type are all these Items? May we see the actual calculation line(s), and how the logging relates to that?

Find out, don’t assume when you have an unexpected problem.

0 + 0 - 10.274 + 5.945 = -4.329
I think your mystery Item was zero at that time.

3

Thanks. This could be the case.
I added that item to the logging and will see if it happens again.