Symbols | Description | |
| System boundary: a rectangular box drawn to represent the boundaries of the system under evaluation. | |
| Pathway: flow of energy, material, or information. | |
| Source: outside source of energy of energy delivering forces according to a program controlled from outside. | |
| Box: miscellaneous symbol to use for whatever unit or function is labeled. | |
| Transaction: a unit that indicates a sale of goods or services (solid line) in exchange for payment of money (dashed line). |