Function check_outright 

fn check_outright(
    code: &str,
    tenor: Period,
    outright: f64,
    spot: f64,
) -> Result<(), RungBuildError>

An FX rung’s outright, refused where it cannot be one: not finite and positive; more than three times spot or under a third of it — forward points, or a quote in other units; or more than 10% from spot and nearer 1/spot than spot — the pair quoted the other way round. A curve solved on either is nonsense, and both are unmistakable against spot, so the rung is refused before anything is solved.