What's meant here by this "GABL" and this whole message?

In "The Blue Scarab" in Dr. Thorndyke’s Case-Book by R. Austin Freeman, Throndyke, who could find the dead body of Uncle Reuben in a meadow based on hieroglyphic letters on a blue scarab and bearings with compass, was reading the translation of letters saying:

"UNKL RUBN IS IN TH MILL FIELD SKS FT DOWN CHURCH SPIR NORTH TEN THIRTY EAST DINGL SOUTH GABL NORTH ATY FORTY FIF WEST GOD SAF KING JORJ."

I could find out the meaning of most words, but I still can’t understand the meaning of "GABL" and "ATY"?

"Uncle Reuben is in mill field six feets down church spire North ten thirty East {Dingle Farm} South GABL North eighty forty five West God save king George".

And what did the numbers refer to?