User blog comment:PurplePenguin/The Grunkle Stan Mystery/@comment-15628758-20130816122127

well,

From what has been seen from Gideion Rises, the books have coordinates to something Stan has recently been working on. The code in the said episode is Search For The Blind Eye. Stan said he has been searching for books 2 (Giedon's book) and 3 (dipper's book). There is no proof Stan has a brother.