"Rate of insured unemployment", for purposes of Section 41-35-330, means the percentage derived by dividing:
- (1) The average weekly number of individuals filing claims for regular state compensation in this State for weeks of unemployment with respect to the most recent thirteen-consecutive-week period, as determined by the commission on the basis of its reports to the U. S. Secretary of Labor, by
- (2) The average monthly employment covered under Chapters 27 through 41 of this title for the first four of the most recent six completed calendar quarters ending before the end of such thirteen-week period.