The raw value of a annual-interest estimation is based on a time-span.
An object of type IDebtFormatter can be used to fomat the annual-interest estimation into man-days, man-months or money.
A Severity level can also be obtained from a AnnualInterest an issue value, through the method IDebtFormatter.IDebtFormatter.ToSeverity. In CQLinq code rule, annual-interest values are obtained by casting explicitly a System.TimeSpan value to an AnnualInterest value, or by naming a TimeSpan column AnnualInterest, in which case TimeSpan values are automatically converted to AnnualInterest values.
Also such annual-interest value obtained in a CQLinq rule context is multiplied by the DebtSettings.DebtSettings.AnnualInterestFactor.

Reference

AnnualInterest Members
NDepend.TechnicalDebt Namespace