Same sound, different spellings
Dictionaries disagree: r vs ɹ, iː vs i, er vs ɚ — all the same sounds. Tap any sound to see its other spellings.
Computers use ALL-CAPS codes for the same sounds (ARPABET, e.g. SH = /ʃ/). Its number marks stress: ER0 = unstressed er (teacher), ER1 = stressed er (bird).