In this Technical Specification, the gravimetric mixture preparation as given in ISO 6142 is investigated for influences of a priori existing, as well as correlations introduced by data processing. All calculations refer to an example which consists in the preparation of a synthetic natural gas of a target composition as follows: 1,4 mol % N2, 1,8 mol % CO2, 9,4 mol % ethane, 3,4 mol % propane, 1 mol % n-butane, and 83 mol % methane. All considerations given for this example concerning mixture feasibility, choice of preparation procedure, and weighing steps and sequences are the same as given in ISO 6142. This also applies to all estimates for basic uncertainty sources and the purity tables of the gases used for preparation. All calculations follow the principles, and use the tools and algorithms laid down in Annex A. For the sake of simplicity, procedural steps such as matrix transformation, inversion or matrix calculus are not detailed each time they are used in the calculations.