The meter processor has a built-in mechanism to avoid negative consumption.
Suppressed Reduction is a buffer that is used when connected meter objects have contribution set to subtract.
The meter values that are included in the calculation does not always arrive at the same time. When meter values that are supposed to be subtracted arrive, they are added to Suppressed Reduction. When a value that is supposed to be added to the result arrives, first the value of Suppressed Reduction is decreased and when the suppressed-reduction value is 0 the rest of the incoming value is added to the result.
For example, if all the meters that add value to the result are offline while values that are supposed to be subtracted arrive, the calculated result will not decrease but remain unchanged until the meters that add values to the result are online again.