ISO/TR 22520:2005 provides comparative data, obtained from various manufacturers and other official sources, for the year 2002, on the A-weighted emission sound pressure levels of portable hand-held forestry machinery. It is applicable to chain saws (for which the existing emission sound pressure levels were for the full range of engine sizes) and to grass-trimmers and brush-cutters. International Standards ISO 11681-1, ISO 11681-2 and ISO 11806 require that these machines be designed to generate noise levels as low as practicable, based on the existing noise emission data, and ISO/TR 22520 is intended to assist in determining compliance with that requirement.