Weibull parameter m can be experimentally identified by two methods: 1) The values of σ σ N measured on many identical specimens are used to calculate the coefficient of variation of strength, and the value of m then follows by solving Eq. (4); or 2) the values of σ σ ¯ ¯ N are measured on geometrically similar specimens of several different sizes D and the slope of their linear regression in the plot of log ⁡ ⁡ σ σ ¯ ¯ N versus log ⁡ ⁡ D gives − − 1 / m . Method 1 must give the same result for different sizes, and method 2 the same as method 1. If not, the size effect is partly or totally non-Weibullian. Omission of testing for different sizes has often led to incorrect conclusions. Another check is that the histogram of the strengths of many identical specimens must be a straight line when plotted in the Weibull scale. A deviation to the right at high strength range means that N e q is too small and the material quasibrittle.