Function align_per_echo_constants 

fn align_per_echo_constants(
    unwrapped: &mut [Vec<f64>],
    tes: &[f64],
    mask: &[u8],
    algorithm: UnwrappingAlgorithm,
)

Remove, from each separately unwrapped echo, the constant its unwrapper leaves undetermined, so that the echoes agree before they are averaged. See field_mapping_direct.