SmartCom Digital System of Units (D-SI) Guide for the use of the metadata-format used in metrology for the easy-to-use, safe, harmonised and unambiguous digital transfer of metrological data - Second Edition (SmartCom数字国际单位制(D-SI):促进便捷、安全、协调、明确的计量数据数字化传输的计量元数据格式使用指南-第二版中文版)