2 Example from OpenIntro Statistics $1.1.2. Standard deviations relative to daily events. Consider a daily event, such as drinking a cup of coffee. For a normal distribution, the data within one standard deviation is about 68% or roughly 2/3. That means 1/3 of the data is outside of this range. Using days as a unit of measurement, 1/3 corresponds to an event that happens once every three days. Data within 30 is about 99.7% and outside this range is about 1/370 or roughly an event that happens once per year. Data within 70 is about 99.9999999997% and outside this range is about 1/390682215145 or roughly an event that happens every 1.07 billion years (roughly four times in the history of earth). From 68-95-99.7 rule on Wikipedia