在计量学和其他科学中，例如化学和物理学，标准是用于校准测量的参考。从历史上看，每个机构都为衡量和衡量系统定义了自己的标准。这导致了混乱。虽然一些较旧的系统仍在使用，但现代标准在国际上得到认可并在受控条件下进行了定义。例如，在化学中，可以使用主要标准作为试剂来比较滴定或其他分析技术中的纯度和数量。在计量学中，标准是定义物理量单位的对象或实验。标准的示例包括国际原型公斤（IPK），其是国际单位制（SI）的质量标准，以及伏特，其是电势的单位并且基于约瑟夫森结的输出来定义。物理测量有不同级别的标准。主标准或主要标准是最高质量标准，它们定义了它们的计量单位。层次结构中的下一级标准是次级标准，其参考主要标准进行校准。层次结构的第三层包含工作标准。工作标准定期从二级标准校准。还有实验室标准，由国家组织定义，用于认证和校准实验室和教育设施。由于实验室标准被用作参考并且符合质量标准，因此它们有时（不正确地）被称为二级标准。但是，该术语具有特定和不同的含义。

英国诺丁汉特伦特大学Essay代写：科学中的标准定义和例子

In metrology and other sciences, such as chemistry and physics, a standard is a reference that is used to calibrate measurements. Historically, each authority defined its own standards for systems of weights and measures. This resulted in confusion. Although some of the older systems are still in use, modern standards are internationally recognized and defined under controlled conditions. In chemistry, for example, a primary standard may be used as a reagent to compare purity and quantity in a titration or other analytical technique. In metrology, a standard is an object or experiment that defines the unit of a physical quantity. Examples of standards include the international prototype kilogram (IPK), which is the mass standard for the International System of Units (SI), and the volt, which is the unit of electrical potential and is defined based on the output of a Josephson junction. There are different levels of standards for physical measurements. The master standards or primary standards are those of highest quality, which define their unit of measure. The next level of standards in the hierarchy are secondary standards, which are calibrated with reference to a primary standard. The third level of the hierarchy encompasses the working standards. Working standards are periodically calibrated from a secondary standard. There are also laboratory standards, which are defined by national organizations to certify and calibrate labs and educational facilities. Because laboratory standards are used as reference and are held to a quality standard, they are sometimes (incorrectly) referred to as secondary standards. However, that term has a specific and different meaning.