Rationale

C 1239 was adopted in 1993. The three authors were: Stephen Duffy then of NASA-Lewis and Cleveland State University, George Quinn of NIST, and Curtis Johnson of GE Corporate R+D Center. This standard was balloted for reapproval in June 2024 at which time a number of equation mistakes were detected. These arose from pdf conversions made by ASTM in the year 2000. These were all editorially corrected in late 2024. A nice improvement to C 1239 would be the addition of simple confidence bands on a unimodal two-parameter distribution graph, our Figure 6. The “bowtie approximation” (a name coined by Andy Wereszczak) adds a visual interpretation that users will appreciate. This is already in ISO 20501:2003 that was prepared by ISO TC 206, Fine Ceramics (Advanced Ceramics, Advanced Technical Ceramics) in 2003 under the leadership of S. Duffy. ASTM C1239 and ISO 20501 are very similar in content. During the ISO process, input from the European community led to the addition of simple confidence bands as recommended below. This proposed revision is easy and will be useful to the user community and C 1239 and ISO 20501 will be in harmony.