TY  - RPRT
TI  - Letter Circular 437: methods of using standard frequency radio emissions (replaces Letter Circular 404)
PY  - 1935
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 437
DO  - 10.6028/NBS.LCIRC.437
ER  -