S.C. Code § 42-1-40
"Average weekly wages" means the earnings of the injured employee in the employment in which he was working at the time of the injury during the period of fifty-two weeks immediately preceding the date of the injury, including the subsistence allowance paid to veteran trainees by the United States Government if the amount of the allowance is reported monthly by the trainee to his employer. "Average weekly wage" must be calculated by taking the total wages paid for the last four quarters immediately preceding the quarter in which the injury occurred as reported on the Department of Employment and Workforce's Employer Contribution Reports divided by fifty-two or by the actual number of weeks for which wages were paid, whichever is less. When the employment, prior to the injury, extended over a period of less than fifty-two weeks, the method of dividing the earnings during that period by the number of weeks and parts thereof during which the employee earned wages shall be followed, as long as results fair and just to both parties will be obtained. Where, by reason of a shortness of time during which the employee has been in the employment of his employer or the casual nature or terms of his employment, it is impracticable to compute the average weekly wages as defined in this section, regard is to be had to the average weekly amount which during the fifty-two weeks previous to the injury was being earned by a person of the same grade and character employed in the same class of employment in the same locality or community.
When for exceptional reasons the foregoing would be unfair, either to the employer or employee, such other method of computing average weekly wages may be resorted to as will most nearly approximate the amount which the injured employee would be earning were it not for the injury. Whenever allowances of any character made to an employee in lieu of wages are a specified part of a wage contract they are deemed a part of his earnings.
S.C. Code § 42-1-40
1996 Act No. 424, Section 13, provides, in part, as follows:
"Section 13. Employers who have filed with the Workers' Compensation Commission a notice to reject the provisions of Title 42 before the effective date of the 1996 amendment will have until July 1, 1997, to comply with the provisions of the 1996 amendment relating to insuring their workers' compensation liabilities. Any employer who has rejected the terms of this title prior to approval of the 1996 amendment and has procured another form of employee benefits insurance shall comply, not later than July 1, 1997, with the provisions of the 1996 amendment relating to the insuring of its workers' compensation liabilities. Furthermore, nothing in the 1996 amendment shall affect or alter any cause of action, right, or claim accruing before the effective date of the 1996 amendment; however, any such cause of action, remedy, or claim accruing before the effective date of the 1996 amendment shall be governed by the law prior to the effective date of the 1996 amendment".