Before answering questions about how stocks change with both in- and outflows you should learn 'graphical integration'. This is three questions that you should alway ask yourself to avoid that your ingrained tendency to think in terms of instantaneous cause and effect influence your questions.

1. In what direction will the stock develop?

- The direction depends on the difference between the inflow and the outflow; that is the net flow.

2. How much will the stock change over a given time period and how large will it be after that period?

- The addition to the stock can be calculated by multiplying the average net flow by the length of the time period. The addition must then be added to the amount in the stock at the beginning of the period.

3. What is the shape of the stock development?

- This 'shape' depends on how the net flow develops over time. As you have seen already, a large net flow gives a more rapid change in the stock than a small net flow.

In the simulator below, you will now control both the faucet inflow and the pump for the outflow. Before you click run, use the questions of graphical integration to find out how the stock will develop. Be aware that it is much easier to come up with an explanation after you have simulated. However, this will also often be a wrong explanation, and you will not realize that it is wrong. When you come up with an explanation before you simulate, you will either learn that you were correct, or you will realize that you were incorrect. The first possibility feels good, the second is very helpful.

Click to open the simulator in a new window.