Each of the eighteen Armanen runes published by Guido von List in 1908 is best understood by asking what he took from the historical record and what he supplied himself.
The character behind it
Ur corresponds to the Younger Futhark character whose Old Norse name was ur, glossed in the Norwegian and Icelandic rune poems as drizzle or slag. The Old English rune poem, working with a different tradition, gives its equivalent the name ur and describes an aurochs. The two glosses do not agree, and that disagreement is old, attested and independent of von List.
What von List did with it
He kept the sound value U, retitled the character in a Germanised form, and assigned it a meaning drawn from his own system rather than from either rune poem. Sixteen of his eighteen correspond to Younger Futhark characters in this way; Eh and Gibor do not, and were added to bring the count to eighteen to match the eighteen charms of the Havamal.
The claim, and its reception
Von List described the row as the recovered alphabet of an ancient Germanic priesthood. Historians of runology do not accept that account, and treat the Armanen row as an early twentieth-century esoteric construction. It was afterwards taken up in volkisch circles and by National Socialist organisations in the 1930s and 1940s. The atlas records that reception plainly, because it is part of what this entry is.