The complete wḏꜣt-eye, showing its hypothesized division into fractional measures.
Traditionally considered to represent a piece of the Eye of Horus or wḏꜣt(literally “Intact One”)
(𓂀), and specifically the pupil of the eye. In Egyptian mythology, the eye was torn out and dismembered by Set, and subsequently pieced back together and restored by Thoth. The series of Egyptian fractional measures of grain would then be either directly based on the pieces of the eye or would have eventually come to be interpreted as such.
In fact, however, while the hieroglyphic signs certainly represent pieces of the eye, their usage as measures is uncertain, as the evidence mainly comes from votive cubits whose texts are extremely difficult to interpret; meanwhile, the hieratic forms of the signs are well attested as measures, but their earlier forms do not closely resemble pieces of the eye. The equivalence of the hieratic and hieroglyphic signs has thus become questionable, and the direct origin of the measures as pieces of the eye is not likely, although their later reinterpretation as such is possible.
James P[eter] Allen (2010) Middle Egyptian: An Introduction to the Language and Culture of Hieroglyphs, 2nd edition, Cambridge: Cambridge University Press, →ISBN, page 106.
Gardiner, Alan (1957) Egyptian Grammar: Being an Introduction to the Study of Hieroglyphs, third edition, Oxford: Griffith Institute, →ISBN, page 451
Ritter, Jim (2002) , “Closing the Eye of Horus: The Rise and Fall of ‘Horus-eye Fractions’”, in J. Steele, A. Imhausen, editors, Alter Orient und Altes Testament, issue 297 (Under One Sky: Astronomy and Mathematics in the ancient Near East), Münster: Ugarit-Verlag, pages 297-323