(a) If at the time of the disability the wages are fixed by the week, the amount so fixed shall be the average weekly wage.

(b) If at the time of the disability the wages are fixed by the month, the average weekly wage shall be the monthly wage so fixed, multiplied by twelve and divided by fifty-two.

(c) If at the time of the disability the wages are fixed by the year, the average weekly wage shall be the yearly wage so fixed, divided by fifty-two.

(d) If at the time of the disability the wages are fixed by the day, hour, or by the output of the employe, the average weekly wage shall be the wage most favorable to the employe, computed by dividing by thirteen the total wages of said employe earned in the employ of the employer in the first, second, third, or fourth period of thirteen consecutive calendar weeks in the fifty-two weeks immediately preceding the disability, or in case the employe receives wages monthly or semi-monthly, by dividing by thirteen the total wages of said employe earned in the employ of the employer in the first, second, third, or fourth period of three consecutive calendar months in the year immediately preceding the disability.

If the employe has been in the employ of employer less than thirteen calendar weeks, (or three calendar months if the employe receives wages monthly, or semi-monthly) immediately preceding the disability, his average weekly wage shall be computed under the foregoing paragraph, taking “total wages” for such purpose to be the amount he would have earned had he been so employed by employer the full thirteen calendar weeks, (or three calendar months) immediately preceding the disability, and had worked when work was available to other employes in a similar occupation, unless it be conclusively shown that, by reason of exceptional causes, such method of computation does not ascertain fairly the “total wages” of the employe so employed less than thirteen calendar weeks (or three calendar months).

(e) In occupations which are exclusively seasonal, and therefore cannot be carried on throughout the year, the average weekly wage shall be taken to be one-fiftieth of the total wages which the employe has earned from all occupations during the twelve calendar months immediately preceding the disability, unless it be shown that during such year, by reason of exceptional causes, such method of computation does not ascertain fairly the earnings of the employe, in which case the period for calculation shall be extended so far as to give a basis for the fair ascertainment of his average weekly earnings.

The terms “average weekly wage” and “total wages,” as used in this section, shall include board and lodging received from the employer, and when so received, the board shall be rated at two dollars per day if more than one meal is served, and one dollar per day if only one meal is served, and lodging shall be rated at one dollar and fifty cents per day. In employments in which employes customarily receive not less than one-third of their remuneration in tips or gratuities not paid by the employer, gratuities shall be added to the wages received at the rate of two dollars per day; but such terms shall not include amounts deducted by the employer under the contract of hiring for labor furnished, or paid for by the employer, and necessary for the performance of such contract by the employe; nor shall such terms include deductions from wages due the employer for rent, and supplies necessary for the employe's use in the performance of his labor.

Where the employe is working under concurrent contracts with two or more employers, and the defendant employer has knowledge of such employment prior to the disability, his wages from all such employers shall be considered as if earned from the employer liable for compensation.

If under clauses (a), (b), (c), (d) and (e) of this section the amount determined is less than if computed as follows, this computation shall apply, viz: divide the total wages earned by the employe during the last two completed calendar quarters with the same employer by the number of days he worked for such employer during such period multiplied by five.

The weekly wage upon which compensation shall be computed, shall be the wage earned by the employe in his last employment in the occupation or industry in which the occupational disease is a hazard.