Areas under the standard normal curve d a variable that has a normal distribution with mean o and variance 1 is called the standard normal variate and is commonly designated by the letter z N(0,1) a As with any continuous variable, probability calculations here are always concerned with finding the probability that the variable assumes any value in an interval between two specific points a and b 14Areas under the Standard Normal Curve  A variable that has a normal distribution with mean 0 and variance 1 is called the standard normal variate and is commonly designated by the letter Z.  N(0,1)  As with any continuous variable, probability calculations here are always concerned with finding the probability that the variable assumes any value in an interval between two specific points a and b. 14