68% piles up near the mean in this bell-shaped curve
Values that vary naturally — like height, test scores, weight — cluster heavily near the mean and get rarer and rarer the further they get from it, tracing a bell shape. This is the normal distribution. Change the mean (μ) and standard deviation (σ) and see how the curve changes, and find out how a standard score interprets a value's position.
The mean (μ) is the center of the curve, and the standard deviation (σ) is how widely the curve is spread. The darker-shaded regions are closer to the mean.
Mean μ70
Standard deviation σ10
Mean ±1σ (about 68%)Mean ±2σ (about 95%)Mean ±3σ (about 99.7%)
A number showing how many standard deviations a value x sits from the mean is the standard score (z-score). It's calculated as z = (x−μ) / σ.