Comments for 真

why is the onyomi written in hiragana? And what does the dash behind ま mean?

The onyomi are the readings that came from China, and the kunyomi are readings that originated in Japan.  Since katakana is [usually] used for foreign or borrowed words, the onyomi is written in Katakana.

I think that the hyphen after ま means that 真 is usually pronounced "ま" when it preceeds another (I assume kanji) characher.  Someone please correct me if I'm wrong about this.

I hope this helps!