TY  - RPRT
TI  - Letter Circular 990: rerefining used crankcase oil (supersedes Letter Circular 360)
PY  - 1950
PB  - National Institute of Standards and Technology
CY  - Gaithersburg, MD
SN  - LCIRC 990
DO  - 10.6028/NBS.LCIRC.990
ER  -