TY - GEN AU - Helmut Hellwig C2 - , National Institute of Standards and Technology, Gaithersburg, MD DA - 1972-01-01 05:01:00 DO - https://doi.org/10.6028/NBS.TN.616r2 LA - en PB - , National Institute of Standards and Technology, Gaithersburg, MD PY - 1972 TI - Frequency standards and clocks ::a tutorial introduction (2d revision) ER -