TY  - RPRT
TI  - Letter Circular 498: methods of using standard-frequency radio emissions (replaces Letter Circular 453)
PY  - 1937
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 498
DO  - 10.6028/NBS.LCIRC.498
ER  -