The mathematical modelling of metals prices is a useful tool for the mining and investment communities by helping to explain market performance. As a service to Mining Journal readers, we provide here an explanation of Bloomsbury Minerals Economics Ltd's model for copper.London-based BME models metals prices with reference to three 'fundamental' forces: stocks of the metal, economic growth (or specific metal demand) and performance of the US dollar. The models have progressed from dealing with commodities as industrial raw materials to dealing with them as a hybrid physical-investment market.BME is this year introducing the influence of investment/disinvestment on the market, and on ways of better understanding investor flows.