The revised International System of Units (SI) came into force on May 20, 2019. Simultaneously, updated versions of supporting documents for the practical realization of the SI base units (mises en pratique) were published. This review paper provides an overview of the updated mise en pratique for the SI base unit of length, the metre, that now gives practical guidance on realisation of traceable length metrology spanning 24 orders of magnitude. The review begins by showing how the metre may be primarily realized through time of flight and interferometric techniques using a variety of types of interferometer. Examples of techniques for measuring the interferometric phase and coping when the integer interference order is unknown are then described, together with examples of typical uncertainty contributions that may be encountered. The requirements for traceable nanoscale metrology and the need for an alternative secondary metre as identified by the Consultative Committee for Length’s Working Group on Nanometrology are outlined. These led to the inclusion in the mise en pratique of secondary realisations of the length unit at the nanometre and sub nanometre scale, based on the lattice spacing of silicon. Three measurement techniques using this secondary realisation are then described in detail. The paper concludes by emphasising that measurements made today over 24 order of magnitude are still compatible with measurements made using the metre as adopted over 200 years ago.

修订后的国际单位制 (SI) 于 2019 年 5 月 20 日生效。同时，发布了用于实际实现 SI 基本单位 ( mises en pratique )的支持文件的更新版本。这篇评论文章概述了更新的实践经验对于 SI 基本长度单位，米，现在为实现跨越 24 个数量级的可追踪长度计量提供实用指导。该评论首先展示了如何使用各种类型的干涉仪通过飞行时间和干涉测量技术来实现该仪表。然后描述了在整数干涉阶数未知时测量干涉相位和应对的技术示例，以及可能遇到的典型不确定性贡献的示例。概述了可追溯纳米尺度计量的要求以及长度咨询委员会纳米计量工作组确定的替代二级仪表的需求。这些导致被列入mise en pratique基于硅的晶格间距，在纳米和亚纳米尺度上二次实现长度单位。然后详细描述使用这种二次实现的三种测量技术。本文最后强调，今天进行的超过 24 个数量级的测量仍然与使用 200 多年前采用的仪表进行的测量兼容。