Sets of letters or numbers, e.g. GST, GPS, USB, CBD, USA, H2O, 021 and 111.
To say the set of numbers out loud, say the first letters or numbers fast and at a low pitch, then slow down and say the last letter or number with a falling pitch.
GSˈT (/dʒi.esˈtiː/; _ _ ╲ )
USˈA (/jɪʊ.esˈeɪ/; _ _ ╲ ).
This is a key feature of Standard English.
It sounds foreign if you stress all the words or numbers equally or if you stress the wrong word or number.