The tablet just gives the lengths of the sides and diagonals. There is no sign of any explicit reasoning on it. The author of the pages linked to from here thin

The tablet just gives the lengths of the sides and diagonals. There is no sign of any explicit reasoning on it. The author of the pages linked to from here thinks that the maker's decision to show both diagonals of the square indicates that it's meant to illustrate a proof. I am not convinced.