The recommendations of the International Telegraph Consultative Committee (CCIT) and International Radio Consultative Committee (CCIR) now extend into virtually every phase of communications, and are becoming of increasing significance to the radio-relay engineer. Of particular interest is the hypothetical reference circuit proposed as a guide for system design. It is pointed out that recommendations with respect to this reference are intended primarily for international circuits, and do not necessarily apply to all operational conditions. Optimum design would suggest that limits be established on the basis of actual performance requirement.