## Methods of calculating targets

You can use any method you like for calculating your targets. Some methods commonly used are:
**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.