Material covered: The ASME Y14.5-2009 standard generally adds new tools or symbols to what already exists in the 1994 version. Because the 2009 standard adds these symbols, drawings completed to the 1994 version may very well still be compliant with the 2009 standard. There are a couple of “changes” that do eliminate some practices in the 1994 standard.
Derived median plane straightness is now derived median plane flatness. This is to say that the maximum material condition modifier can now be used with flatness when controlling the form of a derived median plane. In the 1994 standard, this was done using the straightness symbol.
Another simple change is that the use of the RFS symbol is no longer permitted in the 2009 standard where it was an option in the 1994 standard. The 1994 standard has a well-known issue known as the “tertiary datum issue”, which deals with whether or not a datum feature simulator is fixed in position or spring loaded. The 2009 standard revised the meaning of the material modifiers when used in a datum reference frame to address this issue.