Nearly all CETs have been set politically and not by any elaborate and empirical economic analysis or justification.  The initial CET of the EU Customs Union in 1968 was arrived at through an arithmetic mean of the external tariffs of the then six member States.  The CET of SACU was determined and set by South Africa by simply extending the South African external tariff to the rest of the Union.  The proposed CET of the East African Community was adopted by the Heads of State of the EAC countries, and so was the CET of UEMOA.