The outside diameter of an individual coil winding. This measurement is used as the size of the visual reference circle drawn around each coil on the field heatmap. For a single-coil disc or loop, it's the entire accessory's coil diameter. For a multi-coil mat, it's the diameter of each individual coil, much smaller than the mat's overall width or height. When coil diameter isn't specified, the heatmap estimates it from the distance between detected coils.
Coil diameter is the outside width of a single coil winding, measured straight across. It is the reference circle the heatmap draws around each coil. For a single-coil disc or loop it is the whole accessory; for a mat it is the size of one coil among many, much smaller than the mat itself.
