Normal distribution curve showing standard deviation intervals and their corresponding percentages, used to explain the concept of z-scores.

A bell curve diagram illustrating the distribution of data in a normal distribution, with percentages labeled for different standard deviations from the mean (μ), highlighting the areas within -1σ to 1σ, -2σ to 2σ, and -3σ to 3σ, and emphasizing the 68.2%, 95.4%, and 99.7% rule.