Measurement results contain different kinds of uncertainty. Besides systematic errors and random errors individual measurement results are also subject to another type of uncertainty, so-called fuzziness.
It turns out that special fuzzy subsets of the set of real numbers R are useful to model fuzziness of measurement results. These fuzzy subsets x* are called fuzzy numbers.
The membership functions of fuzzy numbers have to be determined. In the paper first a characterization of membership function is given, and after that methods to obtain special membership functions of fuzzy numbers, so-called characterizing functions describing measurement results are treated.