The provisions of this act shall apply to all taxpayers whose taxable year begins on and after January 1, 1971; provided, however, that in respect to any taxpayer whose taxable year begins in 1970 and ends in 1971, such taxpayer may, at his option, determine his tax under this act or compute his tax liability for such fiscal year ending in 1971, by using the sum of the computations of 1, and 2, as follows:
1. The tax computed under the provisions of the law applicable to the calendar year 1970, multiplied by the ratio of the number of months of the year in 1970, to the total number of months of the taxable year.2. The tax computed under the provisions of this law applicable to the calendar year 1971, multiplied by the ratio of the number of months of the year in 1971, to the total number of months of the taxable year.Okla. Stat. tit. 68, § 2381
Laws 1971, c. 137, § 30, emerg. eff. 5/11/1971.