Final answer:
Corporate treasurers prefer to use market values when calculating debt ratios as they provide a more accurate reflection of the company's current financial position.
Step-by-step explanation:
When calculating debt ratios, corporate treasurers prefer to use market values. This preference is due to the fact that market values of debt more accurately reflect the current economic value rather than historical costs. Companies seek to understand their leverage in the context of the current financial environment, which is why market value, when available, is favored over book, face, or nominal values for a more realistic assessment of the company's financial position.