The solved grid is accepted only when every projection residual is zero. 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 solved grid predicts the measurements
Rows, columns, and the diagonal reproject to the same values: 3, 7, 4, 6, 5.
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Zero residuals accept the image
Every residual is 0, so the reconstruction can be accepted.