Article 14.3 of the Agreement, as amended by the Supplementary Agreement, contains rules for calculating the amount of the partial U.K. incapacity benefit that is payable to persons whose U.K. entitlement is based on Article 14.2 or Article 14.4 of the Agreement and who are also receiving a U.S. disability benefit.  Under this provision, the United Kingdom will first determine the theoretical benefit amount the worker would be entitled to receive if he or she had qualified for invalidity benefits without recourse to the Agreement.  This amount equals the flat-rate amount of Long-term IB plus any increases payable on behalf of dependents or on account of age.  Second, the amount actually payable is determined by multiplying the theoretical benefit by the ratio of the worker’s U.K. periods of coverage to the worker’s total periods of coverage under U.K. and U.S. laws.