This invention concerns the valuation of real estate. In particular it concerns a valuation exchange, and a method of operating such an exchange, to value individual real estate properties and to provide a valuation advice on request. In addition to the exchange performing an electronic valuation process it is able to attach a warranty to the valuation. The invention involves the calculation of statistics from received property sales data. Derived capital growth indices for each area based on the change in sale price of properties that are sold more than once. Derived residuals to describe the distributions of deviations from the capital growth indices. Derived distribution of errors between purchase prices land a range of possible purchase prices, using the residuals. And, an estimated range of property values for each property within the region using the statistics, indices, residuals and errors.