EFT requests can be authenticated by using test keys. A test key is a calculated number that is derived from a series of codes that are contained in a test-key book. The codes in a test-key book represent such variables as the current date, hour of the day, receiving institution, receiving account number, and amount of the transfer. The value derived from these variables equals the test key. The financial institution or corporate customer initiating the transfer will give its EFT information, along with the test-key value. The receiving institution will recalculate the test key and, if the two test keys equal the same amount, the EFT request is considered authenticated. The use of test keys has declined in recent years as more and more institutions impliment personal computer-based EFT systems. (Federal Reserve-Branch and Agency Examination Manual)