TY  - RPRT
TI  - Improved ultrasonic standard reference blocks 
AU  - Eitzen, D G
AU  - Sushinsky, G F
AU  - Chwirut, D J
AU  - Bechtoldt, C J
AU  - Ruff, A W
PY  - 1975
PB  - National Bureau of Standards
CY  - Gaithersburg, MD
SN  - NBS IR 75-685
DO  - 10.6028/NBS.IR.75-685
ER  -