Environmental impact is in general hard to validate. To be able to trust the models is very important that the models are transparent and provide multiple levels of verification. The strategy here is to not calculate everything in the simulation model and instead provide results, which can be verified, to calculate the used resources from. E.g. from the amount of processing time for a machine it is possible to calculate the used energy. From the used resources upstream processes required to produce the resources can be included to get a total emission for the production, e.g. if the emissions to produce one kWh electricity is 0.1 kgCO then the 4 kWh electricity used in a machine give an emission of 0.4 kgCO. The concept is called Level of Equation. The basis is to divide the calculations of environmental impact into 4 levels
* Process times, lead times, idle times, setup times, etc.
* Consumption of resources e.g. Electricity, steal, oil, etc.
* Emissions
* Environmental impact, e.g. [GWP]