ISO 2624:1990

Specifies three procedures for estimating, and rules for expressing, the average grain size of copper and copper alloys consisting principally of a single phase. The comparison procedure (comparing the specimen with a standard chart) is most convenient and is sufficiently accurate for most commercial purposes. In cases of dispute the use of the Heyn or Jeffries procedures (intercept procedure and planimetric procedure, respectively) having higher degrees of accuracy is recommended.