Uncertainty propagation
In order to calculate the error of a quantity derived from a mathematical formula which has measured variables with errors, one should use the uncertainty propagation analysis. If the values of these measured components are uncorrelated then their variances (σ2) have to be taken into account. For correlated variables, their covariances have to be considered too. Here we have the variables (A, B) with uncertainties (σA, σB) and precisely defined constants (a, b).