The following image illustrates the 68-95-99 rule. 68% of the area of the normal curve lies in the region of μ ± 1 s, meaning 68% of data points chosen from this distribution will have values of μ ± 1 s. Similarly, 95% of the area is within μ ± 2 s, and 99 % of the area is within μ ± 3 s.
μ = mean
σ = standard deviation
