The formal definition of large-calibre artillery used by the United Nations Register of Conventional Arms (UNROCA) is "guns, howitzers, artillery pieces, combining the characteristics of a gun, howitzer, mortar, or multiple-launch rocket system, capable of engaging surface targets by delivering primarily indirect fire, with a calibre of 75 millimetres and above".This definition, shared by the Arms Trade Treaty and the Treaty on Conventional Armed Forces in Europe, is derived from a definition in United Nations General Assembly Resolution 46/36L, which set a threshold of 100mm.Several grammatical changes were made to that latter in 1992 and the threshold was lowered in 2003 to yield the current definition, as endorsed by UN General Assembly Resolution 58/54.