IEC 60758:2016 applies to synthetic quartz single crystals intended for manufacturing piezoelectric elements for frequency control, selection and optical applications. This edition includes the following significant technical changes with respect to the previous edition: - order rearrangement and review of terms and definitions; - abolition as a standard of the infrared absorbance coefficient a3410; - addition of the value measurement explanation by FT-IR equipment in annex; - addition of the synthetic quartz crystal standards for optical applications.