The wavelength axis of the spectra shown uses the angstrom, where one angstrom equals:

1. Different parts of the electromagnetic spectrum are quoted in different units. 2. Because the technologies developed for each part differ, for reasons of convenience and historical legacy, different units are typically used. 3. The wavelength axis of these spectra uses the angstrom length unit, where 1 angstrom equals 0.1 nanometres. 4. So ten angstroms make one nanometre. 5. The unit suits atomic-scale distances, which is why crystallographers still use it. _Source: OpenStax Chemistry 2e (CC BY 4.0), Ch 6 'Electronic Structure and Periodic Properties of Elements', sections 6.1-6.5_