rune, is also found on the Stentoften Runestone. There also are some inscriptions suggesting a medieval belief in the magical significance of runes, such as the Franks Casket (AD 700) panel. Charm words, such as , , , and most commonly, , appear on a number of Migration period Elder Futhark inscriptions as well as variants and abbreviations of them. Much speculation and study has been produced on the potential meaning of these inscriptions. Rhyming groups appear on some early bracteates that also may be magical in purpose, such as and . Further, an inscription on the Gummarp Runestone (500–700 AD) gives a cryptic inscription describing the use of three runic letters followed by the Elder Futhark f-rune written three times in succession. Nevertheless, it has proven difficult to find unambiguous traces of runic "oracles": although Norse literature is full of references to runes, it nowhere contains specific instructions on divination. There are at least three sources on divination with rather vague descriptions that may, or may not, refer to runes: Tacitus's 1st-century , Snorri Sturluson's 13th-century , and Rimbert's 9th-century . The first source, Tacitus's , describes "signs" chosen in groups of three and cut from "a nut-bearing tree", although the runes do not seem to have been in use at the time of Tacitus' writings. A second source is the , where Granmar, the king of , goes to Uppsala for the . There, the "chips" fell in a way that said that he would not live long (). These "chips", however, are easily explainable as a (sacrificial chip), which was "marked, possibly with sacrificial blood, shaken, and thrown down like dice, and their positive or negative significance then decided." The third source is Rimbert's , where there are three accounts of what some believe to be the use of runes for divination, but Rimbert calls it "drawing lots". One of these accounts is the description of how a renegade Swedish king, Anund Uppsale, first brings a Danish fleet to Birka, but then changes his mind and asks the Danes to "draw lots". According to the story, this "drawing of lots" was quite informative, telling them that attacking Birka would bring bad luck and that they should attack a Slavic town instead. The tool in the "drawing of lots", however, is easily explainable as a (lot-twig), which according to Foote and Wilson would be used in the same