It is important to address the elephant in the room: ASTM International strictly enforces its copyright. While older standards are sometimes difficult to locate, they are still protected intellectual property.
: Thickness can be measured using various methods, including eddy-current instruments ( ) or microscopical examination ( Availability and Status astm b580-79 pdf
Many university engineering departments or public tech libraries provide free digital viewing access to ASTM databases for members. It is important to address the elephant in