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Method of calculating the GWP referred to in Article 3, point (1), of a mixture The GWP of a mixture is calculated as a weighted average, derived from the sum of the weight fractions of the individual substances multiplied by their GWP, unless otherwise specified, including substances that are not fluorinated greenhouse gases. Σ (Substance × % × GWP) + (Substance Y % × GWP) + … (Substance N % × GWP), where % is the contribution by weight with a weight tolerance of +/– 1 %. For example: applying the formula to a mixture of gases consisting of 60 % dimethyl ether, 10 % HFC-152a and 30 % isobutane: Σ (60 % × 1) + (10 % × 124) + (30 % × 0) Total GWP = 13,0 The GWP of the following non-fluorinated substances are used to calculate the GWP of mixtures. For other substances not listed in this annex a default value of 0 applies. Only emissible components that fulfil broadly the same function are relevant for the calculation of the GWP.