Formulas discussed: Algebra, VBA (Copy, Paste, Select, Range, If..Then..End If, For..Next
The workbook used throughout this post is available here.
When building a model, it is not unusual to, either accidentally or deliberately, build a circular reference. A circular reference is where the result of a formula depends on itself. This could be as simple as B5 = B4+B5, or a complicated loop where cell A references B, which references C, which references D, which references B and E, while E references A, as in the diagram below: