Science Constants - Еngstrцm Symbol: Е Value: 10-10 m Category: - Electromagnetic Constants Description: The еngstrцm is an old unit used for measuring the wavelength of electromagnetic radiation including visible light and X-rays. The unit has since been superseded by the nanometre but is still used in crystallography.   The unit was named after the Swedish physicist A J Еngstrцm (1814-74).