The double-entry system of bookkeeping is prescribed, the accounts being kept on an accrual basis. This Subchapter is written for a manually operated system and the specimen forms are designed for such a system. However, the performance of certain operations by bookkeeping and accounting machines may be found advisable on account of the volume of work or for other reasons. In such cases, it will be necessary to modify the prescribed instructions and forms. The books of account, as prescribed, are those customarily maintained in accounting practice. In order to properly maintain the records, the person designated by the local agency to keep its books should be thoroughly familiar with general accounting practice and should be capable of performing the accounting prescribed. For the most part, the instructions and procedures incorporate the methods and practices followed by most local agencies at the present time. Changes from the existing accounting manual for public housing agencies, issued in 1949, have been made in the interests of clarification and simplification, to reflect changing conditions, amendments to the Public Housing Law, and to reduce the accounting burden on those local agencies operating under Federal, State and municipal aided programs.