In this study, the methods of developing an electro-photographic process which consists of many elements were discussed. There are two approaches. One is to divide the whole system into several sub-systems and individually evaluate the sub-systems. The other way is to evaluate the whole system. The former would be ideal if there were no interactions between the sub-systems. For example, the best toner for the developing process may not be the best for the fixation process. In the study, the latter approach was used to evaluate the whole system. It was clarified from the study that the function of the whole system can be evaluated and part of the system can be optimized at the same time. One of the problems during the study was lack of the reproducibility due to the variation from sources outside the scope of this study. It was resolved by re-examining the noise factors.