The clerk of each circuit court shall receive an annual salary of not more than the salary of a State employee at grade 26, step 20 of the State of Maryland Standard and Bargaining Salary Scale in effect on the day before the day that the clerk begins a new term of office. Any change in the salary paid under the State of Maryland Standard and Bargaining Salary Scale during the term of office of a clerk may not apply to the incumbent clerk, but the changed rate shall take effect at the beginning of the next following term of office. The salary of the clerk of each circuit court shall be set by the Board of Public Works on the basis of the relative volume of business and receipts in the clerk’s office. A clerk shall devote his full working time to the duties of the clerk’s office and is entitled to the salary prescribed in subsection (a) of this section. The salary of a clerk is payable biweekly.