For numerical use the parametric functions described in chapter 5 must be assessed using experimental data. To get a maximum of information, all types of measurements that are quantitatively related to any thermodynamic function of state must be considered. From this dataset quantitative numerical data for the adjustable parameters of the Gibbs energy functions are obtained using the methodology described in chapter 6.

In order to evaluate the reliability and accuracy of the experimental data, it is of great help to know about the various experimental techniques used. Therefore, the main experimental methods in thermodynamic and phase-diagram investigations shall be described here. Nevertheless, this cannot be done here as deeply as in textbooks teaching experimental techniques, for example Kubaschewski et al. (1993).

Here the main emphasis is on how to use various types of data for the optimization and how to connect typical as well as more-exotic measured values with the thermodynamic functions of state.

Since experiments are expensive and time-consuming, all data available in the literature should be sought and their validity checked before one's own experiments are planned. An optimization using only literature data may be a good start, to give an overview, and may reveal, where the knowledge is poor, which further experiments are best suited to fill these gaps. Careful planning of one's own experiments taking this overview into account can very effectively keep the effort involved to a minimum and results in a very significant improvement of the optimization.