calculated on the basis of a reasonable royalty which would have been payable by a licensee or sub-licensee in respect of the registered design concerned. [Para. (d) substituted by s. 78 of Act No. 38 of 1997.] (4) For the purposes of determining the amount of any damages or reasonable royalty to be awarded under this section, the court may direct an enquiry to be held and may prescribe such procedures for conducting such enquiry as to it may seem fit. (5) In any proceedings for infringement the defendant may counterclaim for the revocation of the registration of the design and, by way of defence, rely upon any ground on which the registration may be revoked. (6) Any person who represents that any design is registered, without such representation disclosing the number of the registered design concerned, and from whom the number of such registered design has been requested in writing by registered post by any other person unaware of such number, may not recover from such other person damages, or obtain an interdict against him, in respect of any infringement of such registered design by such other person, committed during the period commencing with the representation and terminating two months after the date on which such other person was notified in writing by the first-mentioned person of the number of the registered design concerned. (7) Any person who, having made a request referred to in subsection (6), expends during the period referred to in that subsection, any money, time or labour with a view to making, using or disposing of any article embodying the registered design or a design not substantially different from a registered design, as the case may be, may apply in the manner prescribed to the court for compensation in respect of the money, time or labour reasonably so expended, and the court may issue such order as it may deem fit. (8) If proceedings are instituted in respect of infringement of a registered design, committed after the failure to pay any prescribed renewal fee within the prescribed period, and before any extension of the period for such payment, the court may, if it thinks fit, refuse to award any damages in respect of the infringement. (9) Nothing in this Act shall entitle the registered proprietor to interfere with or restrain any person performing any of the acts contemplated in section 20 (1) where such person commenced performing any such act before the date of registration of the design. (10) Where a design has been registered, any person who, before the date of registration of that design, expended any money, time or labour with a view to performing any of the acts contemplated in section 20 (1), and who is then prevented from performing any of such acts by virtue of the registration of such design, may apply in the prescribed manner to the court for compensation by the registered proprietor in respect of money, time and labour so expended.