TY  - RPRT
TI  - Letter Circular 621: railway track scale testing service of the National Bureau of Standards fiscal year 1940 (July 1, 1939 to June 30, 1940)
PY  - 1940
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 621
DO  - 10.6028/NBS.LCIRC.621
ER  -