The Heat Flow models allow us to conceptualize heat flow on a thin plate where one is able to describe the exact temperatures on each side and then chart the process of the temperature distribution in real time. There are currently three Heat Flow models. Laplace is the simplest; it fixes the temperature of each edge of the plate and finds the temperature on each part of the plate when it reaches equilibrium. The Poisson model is similar but adds a heat source or sink to any point on the plate. The Diffusion model is like Laplace except that it is also "time-accurate"; that is, it simulates the actual process of gradual heat transfer through the plate over time.