Economics, business, accounting, and related fields often distinguish between quantities that are stocks and those that are flows. What exactly are stock and flow diagrams? A system is a set of interrelating, interconnected parts or elements that, together, generate some distinct outcome or behavior over time. Inventory and Installed Base are examples of stocks. A flow variable is measured over an interval of time. It deals with internal feedback loops and time delays that affect the behaviour of the entire system. Flow is roughly analogous to rate or speed in this sense. In contrast, a stock and flow diagram is a calculable representation of the system. But how exactly do they work? It allows for precise specification of all the system's parts and their interrelation, and provide a basis for simulating the behavior of the system over time. Stocks are entities that can accumulate or be depleted, such as a bathtub, which fills with water from a faucet. And you see that the Casual Loop Diagram is a diagram that proposes which variables are related and illustrates in core feedback and this can also be illustrated in Vensim and there is a separate tutorial for that. Therefore, a flow would be measured per unit of time (say a year). Both diagrams belong to the chapter System Dynamics. Stocks and flows are the foundation of system dynamics modeling. Flows, on the other hand, are entities that make stocks increase or decrease, like a faucet or drain affects the level of water in a bathtub. Define Stocks and Flows and Check Units In the Stock-and-Flow diagram we learned how these variables are related. In dynamical systems modeling, the behavior that the system exhibits over time is called it’s dynamic. Stock and flow diagrams provide a richer visual language than causal loop diagrams, we distinguish between six main kinds of elements: stocks , flows , converters, connectors, sources and sinks. Production (which increases Inventory) a… Stock and flow diagrams visually distinguishe between the parts of the system and what causes them to change. A Stock & Flow Diagram (SFD) is similar to a Causal Loops Diagram (CLD) though provides a more rigourous representation. A stock is measured at one specific time, and represents a quantity existing at that point in time (say, December 31, 2004), which may have accumulated in the past. Stock and flow diagrams, along with the mathematical expressions that specify each construct, provide such a technique. A Stock and flow model helps in studying and analyzing the system in a quantitative way. For this to be possible, each variable must be defined and assigned the correct units, and often new variables must be added as well. These differ in their units of measurement. What is Stock and Flow Diagram? System dynamics is an approach to understanding the behaviour of complex systems over time.