Some Greek Accents and other Diacritics

῾ There's a breathing or h sound

᾽ No Aspiration NO H

´ The ACUTE ACCENT

Its presence or absence and position can show a change of meaning. 

It can appear on any of the last 3 syllables of a word.

Ποτέ means at some time or once but πότε means WHEN

τί means WHAT but τι with no accent means any or some ...

` This is the Grave accent

 and ̆ are used to show if a vowel is long or short in meter and pronounciation.

ᾱ ᾰ ῑ ῐ ῡ ῠ