Prior to October, 1969, Task Group IV of the PVRC Subcommittee on Nondestructive Examination of Pressure Components had formulated PVRC Specification No. 3 entitled Ultrasonic Examination of Forgings. By October 27, 1969, the first revision of this specification had been developed, and was sent to the Task Group members for their evaluation and comments.Revision I differed from the original specification primarily in the use of a side-drill-hole (SDH) calibration standard for shorter test distances and a backreflection (BR) calibration method for longer test distances.In addition, two large calibration blocks, PVRC Reference Block No. 1 by the Bethlehem Steel Corporation and PVRC Reference Block No. 2 by the Midvale- Heppenstall Company, were fabricated for use in conjunction with Revision I.