In law school every American lawyer learns that the conventional measure of damages for breach of a sales contract is the difference between the contract price and the market price. Even before these rules were embodied in the Uniform Sales Act and the Uniform Commercial Code (UCC), they were a staple of Anglo-American common law. They remain the rules with which a court would determine damage liability not only for the sale of goods, but also for the sale of real estate and securities.
White, James J. "The Decline of the Contract Market Damage Model." U. Ark. Little Rock L. J. 11 (1988-1989): 1-19.