Premiums for any policy period shall be paid into the State Insurance Fund at the beginning of the period according to the estimated expenditure of wages for the period. At the end of the period an adjustment of the premium shall be made according to the actual expenditure of wages. If such adjusted premium is more than the premium paid at the beginning of the period, the employer shall pay the difference immediately upon notification of the amount of the true premium paid in advance, the employer shall at his option receive either refund of the difference or a credit of the amount thereof on his account with "The State Insurance Fund."

Laws 1933, c. 28, p. 63, § 1.