def METHOD_NAME(data: list[Datapoint], att: float) -> list[Datapoint]:
    """Correct the ratio for a given attenuation on s21 input"""
    if att <= 0:
        return data
    att = 10 ** (att / 20)
    ndata = []
    for dp in data:
        corrected = dp.z * att
        ndata.append(Datapoint(dp.freq, corrected.real, corrected.imag))
    return ndata