TY  - RPRT
TI  - Circular of the Bureau of Standards no. 27 2nd edition: the properties and testing of optical instruments
PY  - 1918
PB  - National Bureau of Standards
CY  - Gaithersburg, MD
SN  - NBS CIRC 27e2
DO  - 10.6028/NBS.CIRC.27e2
ER  -