TY  - RPRT
TI  - Recent improvements to the ASTM-type ultrasonic reference block system 
AU  - Chwirut, Daniel J
PY  - 1979
PB  - National Bureau of Standards
CY  - Gaithersburg, MD
SN  - NBS IR 79-1742
DO  - 10.6028/NBS.IR.79-1742
ER  -