TY - RPRT TI - Letter Circular 1017: standards for checking the calibration of spectrophotometers (200 to 1000 m?)+J1051:L1051 PY - 1955 PB - National Institute of Standards and Technology CY - Gaithersburg, MD SN - LCIRC 1017 DO - 10.6028/NBS.LCIRC.1017 ER -