ISO/TR 22521:2005 provides comparative data, obtained from various manufacturers and other official sources, for the year 2002, on the vibration emission values at the handles of portable hand-held forestry machinery. It is applicable to chain saws, brush-cutters and grass-trimmers in the full range of engine sizes. International Standards ISO 11681-1, ISO 11681-2 and ISO 11806 require that these machines be designed, based on the state of the art and existing vibration emission data, to generate vibration values as low as practicable, and ISO/TR 22521 is intended to assist in determining compliance with that requirement.