Methods of calculating targets

• Corresponding period the year before
  this is a weak and somewhat unreliable method, based on the assumption that annual seasonal variations are consistent. While that's true for a small number of cases, the big problem is that consumption in the period you're comparing with might itself have been incorrect
• Specific energy ratio
  this method assumes that you use energy or other commodity in direct proportion to the measured product output. Dividing energy used by product output gives a figure for kWh per unit produced, which can then be compared with a target ratio. It's a weak approach because actually there are very few processes which exhibit a constant SER; most SERs are variable because there is always an element of fixed, non-throughput-related, consumption.
• Activity-based target
  the main method propounded in this Guide, this explicitly allows for the fixed element of consumption which SER method ignores. Most commonly it uses a straight-line relationship or multi-factor model as an expected-consumption formula. In its more sophisticated manifestations this approach can deal with complex scenarios, such as irregular batch production, where numerous factors determine the energy requirement in complex and non-linear fashions.