IEC 61300-3-3:2009 describes the procedure to monitor changes in attenuation and/or return loss of a component or an interconnecting device, when subjected to an environmental or mechanical test. Such a procedure is commonly referred to as active monitoring. In many instances, it is more efficient to monitor attenuation and return loss at the same time. This edition constitutes a minor revision. The change with respect to the previous edition is the structure of the document.