First, invoke a 4D-structure model (in this example it is the file Na2CO3-0.MOD). Then from the pulldown menu Modeling select the item Refine Model. A dialog box will appear inquiring the corresponding diffraction data file *.hklm. Select the file Na2CO3.hklm and click OK. A DOS session calculating the initial R-factors will be run, which led to the result shown in the next figure.

In the sub window Least-squares Refinement of the following figure, there are listed all the initial parameters and the initial R-factors. All parameters allowed to be refined are in black, while others are in gray. However all parameters are locked at first. To unlock a parameter, double click on it. This will change its color to red and make it ready for refinement. Upon finished setting parameters and conditions for the refinement, click the button  on the tool bar to start it. The result is show in the next figure

In the following figure, new (refined) atomic parameters are shown in the sub window Least-squares Refinement. Note that the R-factors are changed accordingly. The user may recall previous refinement stages by clicking the button  on the tool bar.

Additional details on structure refinement in VEC are available in on-line Help topics.