*W Markowitz, R G Hall, L Essen, J V L Parry (1958), "Frequency of cesium in terms of ephemeris time", Physical Review Letters, vol.1 (1958), 105–107.
* W Markowitz, R G Hall, L Essen, J V L Parry (1958), «Frequency of cesium in terms of ephemeris time», Physical Review Letters, vol.1 (1958), 105—107.