No Comma. You have a Restrictive phrase (meaning if I delete it, I don't understand the context of the question.) You have a non-Restrictive phrase meaning there should be a comma and if I did delete the 'as shown in he diagram on the left' your answer remains unchanged in its meaning (even if it is wrong.) - Also, I don't see why you need the 'as'. Rewrite: Do you need a comma in this example? No, you don't need the comma, in that example.
It's precisely the "as" that makes the comma necessary. I use no commas in this example, just as I used none in this one. However, as shown here, I do.
Here is the EXACT rule for Adverbable phrases and clauses when using Commas (which using an 'as' makes it an adverb.) Commas with adverb clauses or phrase - When an adverb clause [or phrase] is at the beginning of the sentence, it is an introductory clause and needs a comma separating it from the independent clause. If the adverb clause comes after the independent clause, the conjunction is enough to hold the two clauses together. -From Cingletree Learning, Grammar 101. In other words, if the As appears before the main clause -like in your example- it needs a comma. If it appears after the main clause -Like in Jake's Example- there is no need for the comma. Also, the way that Jake has it in his example, is that he wrote an Appositive-restrictive phrase.
Actually, I'll get to the bottom of this. @Seven Crowns How does 'as' work in regards to Comma usage? To me 'As' makes something an Adverb which means that it doesn't need a comma unless it is in the introductory phrase/clause position. That is pretty much how I understand the rule.
I hesitate to say anything because no one's going to like it. And then I'll be chased by another grammar mob with pitchforks. That sentence isn't what it seems, though it's very elegant in its task. I have an errand to run, but I'll answer when I get back.
This needs a comma. To see why, let's rewrite what you have so that it's a complete sentence and makes logical sense. The first part of the sentence (before the comma) is an independent clause, and the second part is parenthetical, which is why the comma is required. I could just as easily have written the following:
This is not a sentence. The use of "as" here is ambigous, at best, while is not only not a sentence, but also not an example of not using a comma, so it fails to satisfy the query above it. I don't know whether the non-example was deliberately self-contradictory; I simply assumed that it was a joke and followed suit.
