In recent years a series of multivariate control procedures were developed can detecting the variables which are out-of-control. In this paper, one of the most common using and important procedures is discussed, this is the decomposition of T² procedure (MYT procedure). Multivariate control charts using Hotelling's T² statistic are popular and easy to use but interpreting their signals can be a problem. Identifying which characteristic or group of characteristic out-of-control when the chart signals often necessitate an examination of the univariate charts for each variable. This research develops the interpretation of the out-of-control signal. This will be maintained by making an application on the fertilizers factory, i.e. ; one of the most important and biggest factory's in the field of fertilizers. It is important to know that this factory has a special department for quality control; in order to maintain International Standardization Organization (ISO).