Absolute-relative tenses are temporal categories that locate a situation both the some other situation (or topic time) and to an extra-linguistic reference point, typically the moment of speech.
- He had finished his book by yesterday evening.
The English Past Perfect form (had finished) locates the event both prior to an innner-textual reference point (yesterday evening) and to the moment of speech.
Comrie, B. (1985). Tense. Cambridge: Cambridge University Press.