Maintenance of books of account rule prescribes records, professional exemptions, electronic access, and seven-year retention requirements. Maintenance of books of account under section 62 requires prescribed records sufficient for income computation, with special obligations for specified professions, including medical practitioners, and exemptions based on gross receipts thresholds. The rule sets out the required books and supporting documents, defines key terms, prescribes the place and electronic mode of maintenance, and requires retention for seven tax years, with continued preservation where an assessment is reopened.