What is the definition of part to part ratio?

A part-to-part ratio compares different components of a whole in relation to each other rather than to the whole itself. It expresses the relative sizes of two or more parts within a system, often represented as a fraction or a set of numbers (e.g., 2:3:1). This type of ratio is useful for understanding the relationship between various elements, such as ingredients in a recipe or components in a mixture.