However, the award in the present case has no finding of fact as to what the claimant's wages have been subsequent to the injury and therefore no calculation can be made as to the compensation to which the claimant is entitled. Liberty Mut. Ins. Co. v. Goins, 96 Ga. App. 887, 890 ( 101 S.E.2d 920); Mallory v. American Cas. Co., 116 Ga. App. 477 (2) ( 157 S.E.2d 775); Mauldin v. Ga. Cas. c. Co., 119 Ga. App. 406 (3) ( 167 S.E.2d 371). Judgment reversed with direction to remand to the State Board of Workmen's Compensation for further action consistent with this opinion.

3. Although the evidence authorized the finding of subsequent partial incapacity, that part of the award granting compensation on this basis is erroneous. There has been no finding or determination made as to the weekly wages which the claimant is able to earn upon which an intelligent calculation can be made of the compensation to be paid. Colbert v. Fireman's Fund Ins. Co., 112 Ga. App. 187 ( 144 S.E.2d 470); Mallory v. American Cas. Co., 116 Ga. App. 477 ( 157 S.E.2d 775); Mauldin v. Ga. Cas. c. Co., 119 Ga. App. 406, 409 ( 167 S.E.2d 371). The award of partial disability is deficient for another reason. No provision is made reducing the number of weeks of compensation for partial incapacity by the number of weeks for which payment is made for total incapacity as required by Code Ann. § 114-405 (Ga. L. 1963, pp. 141, 146). This part of the judgment which affirms the award of compensation for partial disability must be reversed with direction to remand the case to the board for further action consistent with this opinion.

The employer's remedy, if the employee is not now totally disabled, is by way of an application to the board for a hearing on a change in his condition. Guess v. Liberty Mut. Ins. Co., 219 Ga. 581 ( 134 S.E.2d 783). It is true that the General Assembly amended § 114-709 of the Compensation Act in 1968 (Ga. L. 1968, p. 3) to provide that "change in condition" should mean an economic change occasioned by the employee's ability or inability to return to work, but we have held the amendment to be prospective in effect, thus effective only from and after February 9, 1968. Mauldin v. Ga. Cas. c. Co., 119 Ga. App. 406 ( 167 S.E.2d 371). It can have no effect until a new award is made on the basis of an application for a hearing on a change in the employee's condition. McMullen v. Liberty Mut. Ins. Co., 119 Ga. App. 410 ( 167 S.E.2d 360).

This provision does not apply to the supplemental agreement of March 21, 1967. "The settled rule for the construction of statutes is not to give them retrospective operation, unless the language so imperatively requires." Bank of Norman Park v. Colquitt County, 169 Ga. 534, 536 ( 150 S.E. 841); Leathers v. Turner, 75 Ga. App. 62, 65 ( 41 S.E.2d 921); Mauldin v. Georgia Cas. c. Co., 119 Ga. App. 406. The agreement of March 13, 1967, is controlled by the law applicable to awards and approved agreements made before February 9, 1968. It continues in force until a new award is made upon application on the ground of a change of condition.