Angstrom
The Ångström [ ɔŋstrø: m ] is a named after the Swedish physicist Anders Jonas Ångström unit of length. The unit symbol is Å ( A with ring).
The angstrom is not a SI unit. Since it is not listed in the unit policy, it is not a legal entity in the EU, the Swiss unit regulation also not in Switzerland. In DIN 1301-3 it is explicitly listed as no longer approved unit.
You will still be used in some areas to work with "simple" numeric values can. In particular, in crystallography and chemistry, the Ångström is widespread. 1 Å is the typical order of magnitude for atomic radii, distances of atoms in crystal structures and bond lengths in molecules, the radius of isolated neutral atoms is between 0.3 to 3 Å. For this reason, the Ångström is often used as a unit for distances in atomic sizes, as well as for the specification of the used wavelength of X-rays in their determination in X-ray diffraction experiments such as the crystal structure analysis. Also in the optics or astronomy, the Angstrom is used to indicate a wavelength (though less in German but more in English-language publications).
Here it is shown that 1 Angstrom corresponds approximately to the diameter of an atom.
A similar attempt to come to easy to handle numeric values , undertook in 1925 Manne Siegbahn with the definition of the X - unit, corresponding to about 10-13 m. But this angstrom prevailed.