What is a dimension called that is provided for convenience and is not used for measuring?

A dimension that is provided for convenience and is not intended for measuring is known as a reference dimension. Reference dimensions are typically included in technical drawings to provide additional information or clarify a design intent without serving as a basis for actual fabrication or assembly measurements. They are often used to help the viewer understand the relationship between parts or to provide context for how certain dimensions fit into the overall design.

This type of dimension is distinguished from other dimensions that govern the manufacture of parts. They are indicated in a manner (often italicized) that makes it clear they are for informational purposes and should not be used for fabrication, ensuring that those reading the drawings understand how to use the supplied information appropriately.

The other choices, while they describe various types of dimensions, do not specifically capture the essence of convenience and non-usage for measuring in the same way that reference dimension does.