Thanks in advance
I will forward your question on to the authors.
It is difficult to answer your question. Process capability does not determine process stability - that requires a control chart.
Do you have any statistical software? These calculations were done in the "R" statistical programming language. This is an open source statistics package. Are you familiar with it? The advantage of the method that was proposed in this article is evident for time-based data (e.g., customer response time or process waiting time) where the distribution will never be normal and where using a transformation only slews the graphical plots and makes it difficult for a worker to interpret as the scale is no longer the measurement scale that they are accustomed to seeing. Helping you do this with you data first requires knowing what your data is and what type of process it comes from. These notes here are not long enough to speculate without having data to use for the analysis.