This work discusses the practical use and implementation of a semi-distance based on fuzzy partitions, that allows to introduce expert knowledge into distance computations done on numerical data. It can be used in various kinds of statistical clustering or other applications. The semi-distance univariate behaviour is first studied, then a multivariate clustering case study is presented, that includes an optimization procedure. All calculations are done using the open source softwares FisPro for fuzzy modelling and R for clustering.