(b) The weekly benefit which the disabled employee is entitled to receive for disability commencing on or after May first, nineteen hundred eighty-nine shall be one-half of the employee's weekly wage, but in no case shall such benefit exceed one hundred seventy dollars; except that if the employee's average weekly wage is less than twenty dollars, the benefit shall be such average weekly wage. The weekly benefit which the disabled employee is entitled to receive for disability commencing on or after July first, nineteen hundred eighty-four shall be one-half of the employee's weekly wage, but in no case shall such benefit exceed one hundred forty-five dollars; except that if the employee's average weekly wage is less than twenty dollars, the benefit shall be such average weekly wage. The weekly benefit which the disabled employee is entitled to receive for disability commencing on or after July first, nineteen hundred eighty-three and prior to July first, nineteen hundred eighty-four shall be one-half of the employee's average weekly wage, but in no case shall such benefit exceed one hundred thirty-five dollars nor be less than twenty dollars; except that if the employee's average weekly wage is less than twenty dollars the benefit shall be such average weekly wage. The weekly benefit which the disabled employee is entitled to receive for disability commencing on or after July first, nineteen hundred seventy-four, and prior to July first, nineteen hundred eighty-three, shall be one-half of the employee's average weekly wage, but in no case shall such benefit exceed ninety-five dollars nor be less than twenty dollars; except that if the employee's average weekly wage is less than twenty dollars, the benefit shall be such average weekly wage. The weekly benefit which the disabled employee is entitled to receive for disability commencing on or after July first, nineteen hundred seventy and prior to July first, nineteen hundred seventy-four shall be one-half of the employee's average weekly wage, but in no case shall such benefit exceed seventy-five dollars nor be less than twenty dollars; except that if the employee's average weekly wage is less than twenty dollars the benefit shall be such average weekly wage. For any period of disability less than a full week, the benefits payable shall be calculated by dividing the weekly benefit by the number of the employee's normal work days per week and multiplying the quotient by the number of normal work days in such period of disability. The weekly benefit for a disabled employee who is concurrently eligible for benefits in the employment of more than one covered employer shall, within the maximum and minimum herein provided, be one-half of the total of the employee's average weekly wages received from all such covered employers, and shall be allocated in the proportion of their respective average weekly wage payments.