Readable vs legible

Could you explain what is a difference between readable vs legible?

Which should I use when I want to say "This diagram is easily readable/legible" while meaning - "It is very easy to read and understand meaning of this diagram"?

Dictionaries usually give these as synonyms, but there is a nuance: legible tends to refer only to the presentation, e.g. penmanship, while readable is broader. If what I'm looking at is a hard-to-read scrawl, that's illegible; if it's nicely typed but the grammar and punctuation are all wrong, such that it's hard for me to understand, that's unreadable.

Both legible and readable have sense of "clear enough to read".

Her handwriting was clearly legible.
The figures should be clearly readable

But, readable also may mean "easy, interesting and enjoyable to read".