---
title: What Part of Standards Are Mandatory?
description: It's often very easy to misinterpret essential standards because the difference between mandatory and non-mandatory statements are not always clear.
image: https://blog.q-lab.com/hubfs/FAQ.jpg
---
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# What Part of Standards Are Mandatory?
Posted by [Bill Tobin](https://blog.q-lab.com/author/bill-tobin) on Aug 5, 2022 9:00:00 AM
Standards are a very important part of most weathering and corrosion test programs. Unfortunately, it’s often very easy to misinterpret the intent of a standard because the difference between **mandatory** and **non-mandatory** statements is not always clear.
**Mandatory** statements include words like must, shall, or will in front of verbs. For example: from ASTM G154: “The light source *shall* be fluorescent UV lamps.” This means that an incandescent light bulb can never be used in a test conducted to ASTM G154.
**Non-mandatory** statements include words like should, may or can in front of verbs, or include additional descriptive terms like *preferred, typical, suggested, or about*. This kind of non-mandatory language means that section of the standard can be run a certain way, **but it is not required**. An example of this can be found in ISO 4892-1 in the section describing black standard thermometers: “A typical length and width is about 70 mm by 40 mm.” Use of the words *typical* and *about* means the dimensions are non-mandatory because they are intentionally imprecise.
In addition to mandatory and non-mandatory language, there are a few other rules to keep in mind when reading standards. Different standards bodies use different conventions!
- Notes in ASTM and ISO standards are non-mandatory, unless the note is in a mandatory table
- In ASTM, **Annexes** are mandatory and **Appendices** are non-mandatory
- In ISO, **Normative Annexes** are mandatory and **Informative Annexes** are non-mandatory
In general, Q-Lab strongly recommends that you **read standards in their entirety** to try to understand not only the precise meaning, but also the intent of the writers in cases where the language is ambiguous.
Topics: [FAQ](https://blog.q-lab.com/topic/faq?hsLang=en), [Standards](https://blog.q-lab.com/topic/standards?hsLang=en)
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