Proper way of marking dimensions of a drawing in a paper In a paper I am writing, I will give a figure that shows the mechanical dimensions of a object. I was wondering what the right way to reference the dimensions was, since I have seen multiple ways of this being done.

One way I have seen it done often is with parameters in the drawing, and text describing the values (either in the full text of the figure caption). For example: 



This way offers you the flexibility to talk about the same values in a equation (for example, "It was found that performance was optimal when R1 = D2/2")

An alternative is to have the dimensions directly in the image. This way the reader can just skim through the figures to have an idea about the dimensions, instead of having to read the paper to know them (which can be useful, as often we might want to quickly scan a paper to see if it is what we are looking for before reading it entirely).

This would look like this:



And finaly one could combine the two, and have it say for example "W1 = 7" in the figure. I don't like this that much as it starts to get very messy and crowded very quickly, and lowers the clarity of the figure.

Is there a ''correct'' way to do it?
In my opinion it depends on why the figure is part of the paper.  Say you wont to emphasize a particular set-up , for instance in experimental section or whatever section dealing with experimental details (size and shape ) because necessary for the discussion, then I would explicitly quote the numbers. 

If you are to discuss relation which are general then use letters

If a wish a particular triangle I would cite three numbers. If I discuss Pytagorean theorem is fine and more useful to draw A, B e C.