The closure rule
Over the period measured, the energy in must equal the energy accounted for. If it does not, the ledger is reported as not closed.
The rule
Intake = ΔReserve + Work + Overhead + Waste
The rule follows from the first law of thermodynamics: energy is not created or destroyed. It holds over the measured period T, at the declared meter point.
The closure residual
r = (Intake − sum of accounts) / Intake
The ledger closes if the absolute residual is no larger than the combined relative expanded uncertainty of the measurements, at a coverage factor k = 2.
One account measured independently
At least one account other than Intake shall be measured independently. If Waste were always calculated as whatever is left over, the ledger would close by construction, and the check would prove nothing.
A failed ledger is a result
A ledger that fails closure is reported as "not closed", with its residual. It is never adjusted to fit. The worked examples show a failure and how it was diagnosed.
Questions
What uncertainty is typical?
It depends on the meters. JL-26 requires analyzers with uncertainty of 1% of reading or better at M1 to M3, and facility meters of accuracy class 0.5 or better.
Keep reading
Take the next step.
The closure rule: Intake = ΔReserve + Work + Overhead + Waste, the residual, the uncertainty test, and why one account must be measured independently.