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.