How do I refer to a number in an image in a scientific paper?

Question

I'm note sure if this is the correct place to ask this, but if I have a schematic illustration that contains numbers to enumerate interesting details. How do I refer those numbers in a text that describes this image? Is the following correct?

Figure 3.1 shows (...). It consists of a diffuser (1) that is used (...).

Here point 1 would indicate the diffuser on the illustration. Are there any other ways to refer?

Answer 1

This would seem the most obvious and clear way of referring to details in a picture. I can't think of any better way. I'd do it just like that (1). If you're afraid readers might confuse details with picture numbers, you could use letters (A) or Roman numerals (I) for details instead.