Humboldt Corporation manufactures electronic products, including calculators and printers.
The elements of cost of the company include:

1. Labor in the assembly of a printer
2. Salary of an employee who supervises the manufacture of calculators
3. Materials used in the manufacture of a printer
4. Salary of the president of the company
5. Calculator Division manager salary
6. Depreciation of corporate headquarters building
7. Ink cartridges installed in the printer during manufacturing
8. Depreciation of equipment used in the manufacture of calculators
9. Supplies used in corporate offices

Which of the costs listed above is a direct cost assuming the cost object is a single printer?