The _naagaree-128 Scheme
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Visarg represent an aspiration sound that is somewhat similar to the consonant 'h'. It looks like a colon with Ađhorekhā (ः). Its use is rather limited in Hinđī! Use 'H' to transliterate it. It is easier to pronounce if it is at the end of a word. It is not easy to pronounce it if it is within the word.
Example: छिः (chhiH ~ chhihi), दुःख (duHkh)
10. Om symbol ॐ
As we know, 'ॐ' is the Om symbol, while 'ओम' is a word. According to this key, the word 'ओम' is transliterated as 'Om'. So for representing the 'ॐ' ('the Om Symbol'), we would write '_Om-chihn'. [We may not use the symbol 'ॐ' itself, as this scheme is based on basic latin (as in ASCII 7 bit)].
If the reader (or a reverse transliterator) won't substitute 'ॐ' for '_Om-chihn'; s/he would read '_ओम्-चिह्न'.
You should have read Schwa and Halant.
As we know, a full-form is written with a vowel; while the half-forms are without any vowel and are the pure consonants.
Halant (्) is used to remove the inherent vowel 'a'. In other words, it is typed after a full form of a consonant to make it a half form.
Generally we don't need a Roman/Latin sign to represent the halant! We just take out the inherent vowel 'a'. But if you ever want a Roman/Latin sign to represent/show halant, use '-_' (a hyphen followed by underscore)
Rarely, we would like to explicitly show halant instead of taking out the inherent vowel 'a'! We may be trying to prevent an undesirable conjunct formation! Go thru following examples and decide for yourself whether you will ever need to show the halant!
Ex-1: कम्प्यूटर = kama-_pyooTar (= kampyooTar ;-)
'कंप्यूटर' (kaM-pyoo-Tar; not so bad :-) emphasizes syllable boundaries correctly instead of 'कम्प्यूटर' (ka-mpyoo-Tar).
Ex-2: Another good example is the word 'Hinđī' itself.
It looks like English 'S'. You may use -a- to represent Avagraha 'ऽ'. I may change it while extending _naagaree-128 for Saṅskṛit!
If you find any mistake, PLEASE let me/us know.