From H. W. Smyth, Greek Grammar, I §§149-188
GENERAL PRINCIPLES, ANASTROPHE, CHANGE OF ACCENT IN DECLENSION, INFLECTION AND COMPOSITION, PROCLITICS, ENCLITICS
152. The marks of accent are placed over the vowel of the accented syllable. A diphthong has the accent over its second vowel (τοῦτο), except in the case of capital ᾳ, ῃ, ῳ (as Ἅιδης), where the accent stands before the first vowel.
153. A breathing is written before the acute and grave (οἵ, ἤ), but under the circumflex (ὦ, οὗτος). Accents and breathings are placed before capitals: Ὅμηρος, Ὧραι. The accent stands over a mark of diaeresis: κληῗδι.
154. The grave is written in place of a final acute on a word that is followed immediately by another word in the sentence. Thus, μετὰ τὴν μάχην after the battle (for μετά τήν μάχην). It is also sometimes placed on τὶς, τὶ, to distinguish these indefinite pronouns from the interrogatives τίς, τί.
a. An oxytone changes its acute to the grave when followed by another word, except: (1) when the oxytone is followed by an enclitic; (2) in τίς, τί interrogative, as τίς οὗτος; who's this? (3) when an elided syllable follows the accented syllable: νύχθ' ὅλην, not νὺχθ' ὅλην; (4) when a colon or period follows. (Usage varies before a comma.)
155. The ancients regarded the grave originally as belonging to every syllable not accented with the acute or circumflex; and some Mss. show this in practice, e.g. πὰγκρὰτής. Later it was restricted to its use as a substitute for a final acute.
156. The circumflex is formed from the union of the acute and the grave ( ́̀ = ^), never from ̀́. Thus, παῖς = πάὶς, εὖ = ἔὺ. Similarly, since every long vowel may be resolved into two short units (morae), τῶν may be regarded as = τόὸν. The circumflex was thus spoken with a rising tone followed by one of lower pitch. μοῦσα, δῆμος are thus = μόὺσα, δέὲμος; μούσης, δήμου are = μὸύσης, δὲέμου. In διδοῦσα (i.e. διδόὺσα) compared with διδούς the accent has receded one mora.
a. The whole vowel receives the acute when the second short unit of a vowel long by nature is accented: Δί̄ ̂ Δὶί.
157. Words are named according to their accent as follows:
Oxytone (acute on the ultima): θήρ, καλός, λελυκώς.
Paroxytone (acute on the penult): λύ̄ω, λείπω, λελυκότος.
Proparoxytone (acute on the antepenult): ἄνθρωπος, παιδεύομεν.
Perispomenon (circumflex on the ultima): γῆ, θεοῦ.
Properispomenon (circumflex on the penult): πρᾶξις, μοῦσα.
Barytone (when the ultima is unaccented): μοῦσα, μήτηρ, πόλεμος.
Reference address : https://www.ellopos.net/elpenor/lessons/greek-accentuation.asp?pg=2