100% Rule
The 100% Rule says a parent node's scope must equal exactly 100% of its children's scope combined — nothing missing, nothing counted twice.
What the rule demands
Two things at once: the children summed must reconstruct the parent (no omissions), and no piece of work may appear under two nodes (no double counting). If a "mobile app" node has only "iOS development" and "Android development" beneath it, the rule immediately asks: where does app store review handling live?
Why it matters
It moves scope verification from memory to structure. Ask a review meeting "did we miss anything?" and you get silence. Point at one node and ask "are these children the whole of this parent?" and you get concrete answers. A large share of estimate gaps and scope disputes die at that question.
Using it in practice
Weights are an aid to the 100% Rule, not its proof. Forcing sibling weights to sum to 100 makes you walk the decomposition once more, and it lays the foundation for progress roll-up and simplified EVM (Earned Value Management) — but a sum of 100 does not prove nothing is missing or duplicated. Completeness is still checked by asking "are these children the whole of this parent?" The rule covers completeness at decomposition time; scope that appears mid-project is handled through change control.
wbsgantt auto-distributes sibling weights to sum to 100 and warns right in the editor when they drift.