算出來的normalised SER代表 90 = <= 1 error per 1000 million seeks 80 = <= 1 error per 100 million 70 = <= 1 error per 10 million 60 = <= 1 error per million 50 = 10 errors per million 40 = 100 errors per million 30 = 1000 errors per million 20 = 10 errors per thousand