Intro — Properties:  continued  The mean, µ, is located in the center. The distribution is symmetric about the mean. The mean, median and mode are all equal. The graph is an idealized* representation of the data's histogram...  an illustrative explanation? (*i.e., it has infinite detail or resolution) 68.26% of the graph's area lies over the interval between µ - σ and µ + σ,  95.44% of the area lies over the interval between µ - 2σ and µ + 2σ, and 99.74% of the area lies over the interval between µ - 3σ and µ + 3σ... Key Principle:  The percentage of the data in any interval is equal to the percentage of the histogram's (or the normal curve's) total area which is contained in the portion of the graph which lies over the interval.