This part of ISO 12858 specifies the most important requirements of Invar levelling staffs used in geodesy and industry for precise measurement of heights in combination with either an optical-mechanical level equipped with a parallel plate micrometer, or a digital level of comparable precision. This part of ISO 12858 is not applicable to the detailed design and construction of Invar levelling staffs (e.g. materials, handles, fixing points for the struts, fixing of the Invar strip and of the circular level), which may be selected by the manufacturer as appropriate.