def toStringDuration (duration):
    """Returns a description of the given duration in the most appropriate
    units (e.g. seconds, ms, us, or ns).
    """

    table = (
        ('%dms'      , 1e-3, 1e3),
        (u'%d\u03BCs', 1e-6, 1e6),
        ('%dns'      , 1e-9, 1e9)
    )

    if duration > 1:
        return '%fs' % duration

    for format, threshold, factor in table:
        if duration > threshold:
            return format % int(duration * factor)

    return '%fs' % duration