A central field is computed from a source parameter and radius. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The radius square is part of the source ledger
At radius 4, the checked radius-square is 16.
r2=42=16
The field is mu divided by radius square
The source parameter 16 divided by radius-square 16 gives field 1.