Consideration for know-how: elective spreading of lump-sum into three years for tax inclusion across preceding periods. Where a resident individual who takes more than twelve months to develop know-how may elect that a lump-sum consideration received or receivable for allowing use of that know-how be treated as if one-third of the gross amount were included in his income chargeable to tax for the year of receipt and for each of the two immediately preceding previous years, and assessments for the two preceding years, if made, are to be rectified under the rectification provision with the limitation period reckoned from the end of the financial year in which the assessment relating to the year of receipt is made.