Should I use 1A or 2.1 A ?

1A stands for "first-level" or "primary-level" heading, while 21A stands for "second-level" or "secondary-level" heading.

In general, 1A is used for main headings and subheadings that are at the forefront of the article, while 21A is used for more specific subheadings that support the main content.

For example, if you are writing an article on a complex technical topic, you might use 1A for the main heading and 21A for subheadings that explain the technical details. On the other hand, if you are writing an article on a topic that is more straightforward and has few technical details, you might use 1A for the main heading and 1A for subheadings that provide an overview of the topic.

In conclusion, the decision of whether to use 1A or 21A in your writing will depend on the nature of your article and the audience you are trying to reach. As with any writing, it is important to choose the format that will make your article the most effective and easy to understand for your readers.