Further classification using tag duration (time level) is useful in making a decision as to which tag type is suitable for each material type.
The proposed material types here can be categorised into permanent, removable and disposable types.
A permanent type of tags is used if ILM is a longer process, whereas removable and disposable typed are used if ILM needs simple tracking like one or two stages in Fig. 2.
As this study emphasises the simplification of material types, time level for material types is beyond its scope. Nevertheless, this paper provides some discussion about the time level in site trials.