2. Where an employee is engaged in continuous employment, the exemption per pay period is:(a) in the case of the usual period for which the employee is paid, the quotient obtained by dividing the basic exemption for the year by the number of times the pay period would occur in the year if its length were the same for the entire year;
(b) where there is no usual period for which the employee is paid, the portion of the basic exemption for the year that the number of days contained in the pay period or since the beginning of the year is over 365, whichever is the earlier date.