2021BS EN IEC 61828:2021 Ultrasonics. Transducers. Definitions and measurement methods regarding focusing for the transmitted fields
2002BS EN 61828:2002 Ultrasonics - Focusing transducers - Definitions and measurement methods for the transmitted fields
BS EN IEC 61828:2021 Ultrasonics. Transducers. Definitions and measurement methods regarding focusing for the transmitted fields was changed to BS EN 61828:2002 Ultrasonics - Focusing transducers - Definitions and measurement methods for the transmitted fields.