The COALPW indicator is computed by taking the ratio of coal energy (IEA_TLCOAL) to the total energy supply, where total energy supply is the sum of all constituent energy sources:

COALPW = goalpost(IEA_TLCOAL / (IEA_TLCOAL + IEA_NATGAS + IEA_NCLEAR + IEA_HYDROP + IEA_GEOPWR + IEA_BIOWAS + IEA_FSLOIL), 0, 0.4)

This produces a value between 0 and 1 representing the percentage of total energy supply from coal sources. The score is then calculated using goalpost transformation with lower goalpost of 0.40 and upper goalpost of 0.0 (inverted indicator).