The GRAFIX Control Block (GCB) is a structure which can be appended to any ASTERIX binned dataset and which contains attributes which control the way the GRAFIX system plots the contents of that dataset. Applications are provided within ASTERIX to edit the attributes but they may also want to be set directly by user applications. For example an application that produces a frequency distribution may wish to set the appropriate attribute such that the dataset produced gets plotted by default in a histogram style. All manipulation of the attributes is done through subroutines and the following is a description of those subroutines. A description of the objects within the GCB is also provided but applications should not make direct reference to these as they may change in the future.