1.1 ,This guide covers general procedures for the material selection and fabrication of reference blocks made of metal or metal alloys and intended to be used for the examination of the same or similar production materials by pulsed longitudinal ultrasonic waves applied perpendicular to the beam entry surface. Primary emphasis is on solid materials but some of the techniques described may be used for midwall examination of pipes and tubes of heavy wall thickness. Near-surface resolution in any material depends upon the characteristics of the instrument and search unit employed.