# How to read a graph

On this graphic, there is an arrow from node A to node B if B needs A to be computed. A square node means taht it’s a constant, a circle node means it’s a variable.

Colors corresponds to sectors, which are listed below:

- Persistent pollution sector
- Population sector
- Capital sector
- Agricultural sector
- Nonrenewable resource sector
- World3 03 supplementary equations sector
- World3 03 indicators sector