Canada Countback Method DSO Calculation

[Dimplejuneja]

What does it mean to be less than zero days when using the Countback DSO method? For example: Net accounts receivable for the current month (Nov) are: $1,800, Current month revenue (Nov) is $4,600 and Prior period Net revenue (Oct) is 2,700. Using the countback method, DSO is calculated is (1800-4600)/2700*31+30= Negative two days. How should this be interpreted in terms of a company's collection ability?