Exponential Distribution probably density function NIST Exploratory Data Analysis NIST Exploratory Data Analysis NIST/SEMATECH e-Handbook of Statistical Methods cumulative distribution function NIST/SEMATECH e-Handbook of Statistical Methods Percent Point Function NIST Exploratory Data Analysis NIST Exploratory Data Analysis NIST Exploratory Data Analysis NIST Exploratory Data Analysis NIST Exploratory Data Analysis NIST Exploratory Data Analysis