33. The expert from EC reiterated the importance of the Unique Identifier (UI) and DETA for the simplified lighting and light-signalling Regulations (GRE-77-31). According to him, the grouping of a number of devices into a single Regulation is not compatible with the traditional approach of using one marking per series of amendments to the Regulation. Thus, he argued in favour of mandatory, rather than optional, use of UI. GRE concurred with his view, but noted that the use of UI is conditional upon the availability of DETA. The expert of GTB also pointed out the unclear interpretation of Schedule 5 to the Revised 1958 Agreement with regard to the obligatory use of UI and DETA.