This paper describes a general mechanism for the qualitative interpretation of simple arithmetic relations. This mechanism is useful for the understanding and reasoning about domains that can be modeled by systems of simple arithmetic equations. Our representation attempts to model the underlying arithmetic in its complete detail. Reasoning from these forms provides the completeness and consistency that cannot be always guaranteed by a pure production-rule based system. We describe an experimental architecture for Equation Reasoning (ER), and illustrate its applicability using examples from the financial domain.