While the principle upon which earned profits on subdivision sales are determined is simple (See SectionSection 144, 145), difficulties often arise in practice. For instance, it frequently happens that a tract of land is divided into hundreds, or even thousands, of subdivisions - either farms or lots - and the number of purchasers also runs into the hundreds or thousands, each purchaser necessarily having his own account in a sub-ledger. Under such conditions, the payments are usually small, sometimes as low as one dollar a month, which makes it impracticable to compute the earned profit on each payment or on each contract, unless there has been adopted some method similar to that described in Section 174. If such a method were adopted, profits would be arrived at by basing calculations on totals and averaging the results. For this the following facts are necessary: (1) cost price; (2) selling price; (3) profit, i.e., selling price less cost price; (4) payments actually made. Having these we can readily solve the equation:

Payments made / Total purchase price X total gain = earned profits

The question then is, how best to obtain these figures, as they seldom appear on the face of the books found in real estate offices,