A producer of ham salad may like to know how the environmental load of his product changes if the content of ham in the salad is slightly increased or decreased. 

The question can be answered by analyzing marginal changes in the ham's product chain as a result of the producer's marginal change in ham demand.

The marginal change in demand for ham will cause a marginal change in all processes in the ham's product chain because all ham production production processes are regulated by the market. However, pigs are produced in many different types of farms and different farms will react differently to changes in market demand. Thus, data on pig production are derived from the marginal pig farm, namely the farm which is most likely increase or decrease its production as a result of the marginal change in market demand.