Normal distribution and the σ rules
Set μ and σ of the Gauss curve and use the σ rules 68.3 %, 95.4 % and 99.7 %.
- Germany: grade 12
- Palestine: grade 11
Guide
Many quantities, such as body heights or the measures of workpieces, are spread in a bell shape around a mean. The Gauss curve describes this normal distribution with the expected value μ and the standard deviation σ.
μ fixes the position of the maximum, σ the width: a larger σ makes the curve wider and flatter. The area under the curve is always 1 (100 %).
σ rules: in the interval [μ − σ; μ + σ] about 68.3 % of the values lie, in [μ − 2σ; μ + 2σ] about 95.4 % and in [μ − 3σ; μ + 3σ] about 99.7 %.