TY - RPRT TI - Letter Circular 509: railway track scale testing service of the National Bureau of Standards fiscal year 1937 (July 1, 1936 to June 30, 1937) PY - 1937 PB - National Institute of Standards and Technology CY - Gaithersburg, MD SN - LCIRC 509 DO - 10.6028/NBS.LCIRC.509 ER -