1966 · J.H. Armstrong, P.R. Blomster, et al. · Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS) · 10
1975 · R.N. Castellano, J.L. Hokanson · Joint Conference of the European Frequency and Time Forum and IEEE International Frequency Control Symposium (EFTF/IFCS) · 8