Maintenance of accounts required for specified professions and threshold-exceeding businesses; Board empowered to prescribe rules and retention. Insertion requires maintenance of accounts by specified professions and by businesses or professions that exceed statutory income or turnover thresholds or are likely to do so in a year; the Board may, by rules, prescribe the books and documents to be kept (including inventories), the particulars, form, manner and place of maintenance, and the retention period to enable the Income-tax Officer to compute total income.