Accuracy evaluation of a cesium fountain primary frequency standard at NIST. - D. M. Meekhof; Steven R. Jefferts; M. Stepanovic; Thomas E. Parker (IEEE Trans. Instrum. Meas., 2001)

Recent improvements in NIST-F1 and a resulting accuracy of δf/f=0.61×10-15. - Thomas P. Heavner; Steven R. Jefferts; Elizabeth A. Donley; Jon H. Shirley; Thomas E. Parker (IEEE Trans. Instrum. Meas., 2005)