A technique introduced by Jacobsen (1927) as a graphical method for determining mixing coefficients in a T–S diagram. It was extended by W¨ust in 1935 who developed his core layer method. This was further extended by Tomczak (1981) who developed a multi–parameter analysis technique by adding oxygen and nutrients as additional quasi–conservative parameters. This idea was further developed into what is currently known as Optimum Multiparameter Analysis (OMP).