The report classifies a coil as a focused disc or a spread donut from the shape of its measured field.
Where it appears in the report: Coil characterization
The evidence
A coil reads as a donut when its field peaks in a ring away from the center by a wide enough margin, and as a disc otherwise. The exact margins are our convention, applied the same way on every report so the classification stays consistent.
How the wire is wound sets where the field is strongest. Each profile is a real measured cross-section. A pancake coil is a tight flat spiral, so its field stays strong across a broad center. A donut coil leaves a hole in the middle, so its field peaks in a ring and dips at the center. A loop coil is one large turn, so its field peaks over the wire ring and eases off toward the middle and the rim. Copper dots are the wire seen end-on.
