This part of IEC 61753 contains the minimum initial test and measurement requirements and severities which a fibre optic middle-scale 1 x N (16 ≤ N ≤ 64) DWDM (Dense Wavelength Division Multiplexing) device with channel spacing of 50 GHz, 100 GHz and 200 GHz needs to satisfy in order to be categorized as meeting the requirements of category C-controlled environments. The requirements cover devices with single-mode non-connectorized pigtails and no circuit board. There is also a distinction between small-scale (N < 16) and large-scale (N > 64) 1 x N DWDM devices for the purpose of this standard.