def human_m(v):
    """Returns a distance autoselected for mm, cm, m, and km
    """
    if v < 0.01:
        return v * 1000.0, 'mm'
    if v < 1:
        return v * 100.0, 'cm'
    if v < 1000:
        return v, 'm'
    return v / 1000.0, 'km'
