Atomic timekeeping services started experimentally in 1955, using the first caesium atomic clock at the National Physical Laboratory, UK (NPL).
ɐtˈɑːmɪk tˈaɪmkiːpɪŋ sˈɜːvɪsᵻz stˈɑːɹɾᵻd ɛkspˌɛɹɪmˈɛntəli ɪn nˈaɪntiːnhˈʌndɹɪd fˈɪfti fˈaɪv, jˈuːzɪŋ ðə fˈɜːst sˈiːsiəm ɐtˈɑːmɪk klˈɑːk æt ðə nˈæʃənəl fˈɪzɪkəl lˈæbɹətˌɔːɹi, jˌuːkˈeɪ ˌɛnpˌiːˈɛl.