Armstrong intended to say "That's one small step for a man", but the word "a" is not audible in the transmission, and thus was not initially reported by most observers of the live broadcast.
ˈɑːɹmstɹɔŋ ɪntˈɛndᵻd tə sˈeɪ "ðæts wˈʌn smˈɔːl stˈɛp fɚɹə mˈæn", bˌʌt ðə wˈɜːd "ˈeɪ" ɪz nˌɑːt ˈɔːdᵻbəl ɪnðə tɹænsmˈɪʃən, ænd ðˈʌs wʌz nˌɑːt ɪnˈɪʃəli ɹᵻpˈoːɹɾᵻd baɪ mˈoʊst əbzˈɜːvɚz ʌvðə lˈaɪv bɹˈɔːdkæst.