The probability of normal R.V. with absolute Value less then and equal to one, two, and three unit standard deviations are calculated from error function, the cumulate probability distribution of normal density.

• 常态分布随机变数绝对值小于等于一个、两个、三个标准差之机率分别代入累积机率分布函数(误差函数)算出其对应之机率。