1. Study the historical economic relations between Africans and Europeans 2. Estimate the "fair" rates of interest, exchange, returns, etc. 3. Establish the actual rates of interest, returns, etc. 4. Estimate the difference between the fair and actual rates--this will be the amount needing repair. 5. Estimate the present value of the reparations using compound interest. 6. Devise means of repair.
See his essay in Thomas Boston's _A Different Vision_, Routledge.