Function sweeps_exhausted 

fn sweeps_exhausted(
    scheme: Interpolation,
    sweeps: usize,
    solves: &[PillarSolve],
    rungs: &[Rung],
    fallback: NaiveDate,
) -> CalibrationError

A fit still moving when its sweeps ran out, named by the rung left worst off (or fallback, for a ladder with no solves to name).