With the command Objects|Master parameters (in the main window of SCOUT) you can open the list of so-called master parameters which collects parameters that can be used to control other parameters of the model. Master parameters have a name, a value and a number of decimals. The following restrictions apply to the name: It must not contain any spaces and its length must be below 30 characters. As all other parameters, master parameters can be fit parameters. Just drag them to the fit parameter list or select them in the 'Fit parameter selection' dialog.

Any fit parameter in the fit parameter list can be computed from the values of the master parameters. In this case such a parameter is called slave parameter. To turn a fit parameter into a slave parameter move the cursor to the column called 'Variation' which usually shows the 'Downhill simplex'entry. Now press F4 and see that the cell content changes between 'Downhill simplex', 'Frozen', various 'Grid' items and an empty content. Select the empty state and type in a formula which may contain the names of the master parameters. This way the parameter is computed from the master parameter values. It is not varied directly in the fit routine, and you cannot use a slider to change its value.

Applying master and slave parameters you can describe a coupling between model parameters. If, for example, the damping constant of a Drude model for free electrons in a thin metallic film depends on the film thickness, you can define a master parameter called 'Thickness'. This master parameter can control both the damping constant of the Drude model and the film thickness by appropriate expressions in the list of fit parameters.