New IEEE Standard - Active. This standard provides uniform measurement procedures for determining the shielding effectiveness of electromagnetic (EM) shielding for a variety of enclosures and boxes having all dimensions between 0.1 m and 2 m in the radio frequency range not addressed by IEEE Std 299(TM)-2006. This standard is divided into two parts: Part I - 0.75 m to 2 m and Part II - physically small (< 0.75 m) but electrically large enclosures. In addition to a number of annexes aiding the measurement of shielding effectiveness of these enclosures, Annex I addresses physically small and electrically small enclosures, and Annex J addresses electrically small enclosures in reverberation chambers. Problems occurring in the testing of small enclosures having linear dimension less than 2 m are very different from determining the shielding effectiveness of large rooms and broad depending on the actual size of the enclosure itself. A number of other annexes are included that address rationale, mathematical formulas, selection of measurement techniques, preliminary measurement and repairs, wall-mounted monopoles, impedance mismatch correction, and using isolated monopoles in outer reverberation chambers.