TY  - RPRT
TI  - Letter Circular 1039: NBS standards for opacity meters (supersedes Letter Circular 418)
PY  - 1961
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 1039
DO  - 10.6028/NBS.LCIRC.1039
ER  -