Although Reality Check equations in Vensim have been implemented as an extension of the Vensim modeling language, the skills and experience required to write Reality Check equations is different from that required to write models. Reality Check equations are assertions about the nature of behavior in reality. They do not require the creation of structure capable of generating particular behavior. Reality Check equations create behavioral conditions and then check to see if the structure of the model causes the appropriate behavioral response.
Because Reality Check equations are formulated in a behavior-behavior world, the people best at formulating them are the people with the most knowledge of behavior—for the most part experts in the domain of study. Because of this, Reality Check equations can do much more than find bugs in models. Reality Check equations allow the consumers of models to have confidence in the quality of the results they are getting.