standard length bar的意思|示意

For many years, the scientific standard of length was a metal bar kept in a temperature controlled vault near Paris.

多年来，长度的科学标准曾是一根金属棒，这根金属棒保存在巴黎附近的有温度调节的地下室里。

The reference standard, of convenient length, shall be prepared from a length of bar or tube of the same nominal outside diameter, material and heat-treatment as the material examined.

对比试块应从与待检材料有相同的公称外径、材质和热处理状态的棒或管上制取。