This chapter examines the connection between Heidegger’s analysis of assertions and the present-at-hand. It argues that Heidegger does not claim that assertions can only intend present-at-hand entities. Only in limiting cases, after a changeover in our understanding of being, are assertions so constrained. There are both textual and phenomenological grounds for this argument. Phenomenologically it is evident that many assertions are part of circumspective and absorbed dealing with equipment. The textual argument lies in an interpretation of Heidegger’s underdeveloped notions of unthematic understanding and the changeover. The chapter draws on Aron Gurwitsch’s phenomenology of thematic fields and argues that the changeover, in Being and Time, functions like a figure–ground switch. An upshot of the argument is that there is no paradox in Being and Time making assertions about entities that are not present-at-hand. It also explains Heidegger’s careful methodological considerations about how to thematize and grasp these entities phenomenologically.

In this chapter, we discuss how to model additional processing features that may be present in a chemical facility. To keep the presentation simple, we illustrate how models based on a common discrete grid can be modified to account for these features. Continuous time models can also be extended to account for most of these features, but often lead to more complex and/or nonlinear formulations. We start, in Section 8.1, with the modeling of material consumption and production during the execution of a batch. In Section 8.2, we discuss the modeling of complex material storage and transfer activities. In Section 8.3, we present how to account for unit and task setups and task families. Finally, in Section 8.4, we present how to model unit deterioration and maintenance tasks.