Error macros generate an error message to the console and an error message in the listing. Both the text that caused the error and the result of its evaluation are displayed in the generated error message:
| Macro name | Description |
| errnz | Evaluates a given expression. If the result is not zero, an error is displayed. |
| errn$ | Subtracts the offset of the label parameter from the offset of the location counter and then adds the bias parameter to the result. If this result is not zero, an error message is displayed. |
Error macros let you code assertions into an assembly-language source program. This enables you to code optimum instruction sequences for some operations based on the variable allocation or bit position of a flag in a word and assert that the assumptions made are true.