This chapter deals with the problems and methods for building an observable event that implements an action Model of Reality in the 1st-person perspective. Since “Reality” in Conscious Action Theory (CAT) is a structure of activity, it is the activity in the brain of a human mathematician or in the electronics of a modern computer, not the answers resulting from those activities that model Reality. The CAT model starts with an empty book and a pen filled with ink. The movement of ink executed from the first to the last side is an activity that can be witnessed by the 1st-person observer from the outside. The introduction of permanent ink as the record of change and book coordinates as the location of endpoints in the emptiness of the book defines support components that allow the model creator and user to build and manipulate the model.