I should really add the explanation for the quality levels somewhere 
天 means that all readings of a compound match
上 means that the main reading matches, but you can also read it in a way not covered by the tone mark, but rarely
中 means that the main reading is different (かん here), but at least one of the phonetic readings is also used as a reading for the kanji (けん), just not in first place
下 means that the phonetic readings are nowhere to be found.
Kanjipedia: けん is a non-jouyou reading:
