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as a time adverb as far as I know since can be used in these ways:

1- Present Perfect//since//Simple Past

She's lost over 20 Ibs in weight since she started that diet.

2- Past Perfect//since// Simple Past

The place had completely changed since I went there three years ago.

3- Present Perfect Continuous//since//Present Perfect

She's made a lot of friends since she's been living here.

4- Past Perfect//since//Simple Past

Yesterday Bobby told me he hadn't eaten since Tuesday.

but the sentence below is against the rule. can you explain the reason why simple past//since// past perfect is used in the sentence?

He ate well for the first time since he had left the camp for his last shift of work

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I know I'm not answering your question, but 3. doesn't seem correct to me. I would write "since she started living here/since she moved here". I can't find an example where "since" is used with the present perfect (in the meaning "from the moment, day, year... when). It refers to a precise moment in the past, and the correct tense is the simple past.
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All I can say, as a native speaker, is that no.3 (She's made a lot of friends since she's been living here) is commonly heard. I think Pieanne has a point, though, from the grammatical/semantical angle. Since would have to be understood as during the time; I don't know if that is officially viable.
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That sentence you are referring to is from Longman Contemporary English, Pieanne. I find it hard to understand why we need to say that instead of what you said, too. A native speaker can clarify these for us I think.
Oh! Well, it just doesn't seem right to me but yes, let's wait for a native...
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 davkett's reply was promoted to an answer.
thank you davkett and pieanne.

but what about this?

He ate well for the first time since he had left the camp for his last shift of work

it comes to me since has been used here as if it were "after".

Alice felt more independent after she had learnt to drive.

am I right?

or is "since" not an adverb of time here but an adverb of reason?

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