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Pool or dump
A window is matched or it is a dump into the bank.
Calum reads remaining clearance against draft marks we paint on the sill, not against a feeling in the hands.
Matched pool
Ball clears the sill. Bank stays dry. We leave the miters locked.
Low fill
Clearance remains, window rounding. Hold if the face still has loft to give. If not, shut.
Dumped
The marks sit under water. A higher number on a screen will not lift a dead pool. We write shut on the card.