Whereas Persian and Urdu use three diacritics (rarely written) as well as three letters to represent their 6 vowel sounds, Rohingya has been modified to eliminate the reliance on such a dual system, instead solely relying on diacritics.
10 of these letters are exclusively used in writing of loanwords from Arabic or from European languages.
Unlike parent system, Persian and Urdu, Rohingya cannot be written or read without diacritics.
6 Tanween (double) diacrictics are also used to represent the post-nasalized versions of the 6 vowel sounds.
Historically Arabic script has been adopted and used by many tonal languages, examples include Xiao'erjing for Mandarin Chinese as well as Ajami script adopted for writing various languages of Western Africa.
This is important to note, as without the diacritic present, there is no way to distinguish between tone markers and I‘jām i.e. dots that are used for purpose of phonetic distinctions of consonants.
The Hārbāy (represented with diacritic ◌𐴤 in Hanifi script, and with an acute accent ◌́/á in Latin): a single dot that's placed on top of Fatḥah and Ḍammah, or curly Fatḥah and curly Ḍammah (vowel diacritics unique to Rohinghya), or their respective Fatḥatan and Ḍammatan versions, and it's placed underneath Kasrah or curly Kasrah, or their respective Kasratan version.
[1][2] The Ṭelā (represented with diacritic ◌𐴥 in Hanifi script, and with double vowels with acute accent on the first; ◌́◌/áa in Latin):, is two dots that are placed on top of Fatḥah and Ḍammah, or curly Fatḥah and curly Ḍammah, or their respective Fatḥatan and Ḍammatan versions, and it's placed underneath Kasrah or curly Kasrah, or their respective Kasratan version.
[1][2] The Ṭāna (represented with diacritic ◌𐴦 in Hanifi script, and with double vowels with acute accent on the first; ◌◌́/aá in Latin), is a fish-like looping line that is placed on top of Fatḥah and Ḍammah, or curly Fatḥah and curly Ḍammah, or their respective Fatḥatan and Ḍammatan versions, and it's placed underneath Kasrah or curly Kasrah, or their respective Kasratan version.