revaluation

sir I did not understand the journal entry for revaluation increase and decrease. example. land book value is 13000 . two years ago a slump in land values led to reduce CV from 15000. now, land worth 20000. I did journal entry as dr ppe 7000 cr revaluation surplus 7000 but the correct entry was dr PPE 7000 cr p/l 2000 cr revaluation surplus 5000 sir I did not understand how these values are adjusted in journal entry