3.7.3. Between-method variance and method weights
If all measurements are unbiased and independent, then it is well known that using a weight for each measurement that is inversely proportional to its variance leads to an unbiased estimate of the true value with minimum variance [[15], [16]]. The measured values produced by each method are modeled as the sum of the true property value, method bias, and random error, as described by Eq. (15).