7 使用国际单位制的平衡当量浓度。对于氡照射的大多数历史测量，以及现有测量都是以所谓的月吸入剂量（WLM）来表示的。1WLM 相当于 0.637 MBq h m-3。
7 Equilibrium equivalent concentration using Système International (SI) units. Most historic, and indeed current, measurements of exposure to radon in mines are expressed in terms of the so-called working level month (WLM). 1 WLM is equivalent to 0.637 MBq h m-3.