When completed, the sum of all the numbers of 'each' of the horizontal rows, vertical columns and both diagonals will add up to 34 .
then, very lightly draw 2 diagonal lines across the entire main SQUARE >>>
When inserting the first group of red numbers, start counting from the top left corner -- with the number 1, and on forward to the number 16 -- and put in only those numbers that can be placed into the squares that do not have part of the diagonal lines running through them .
When inserting the second group of red numbers, again start counting from the top left corner -- only now, with the number 16, and on backwards down to 1 -- only now, you will put these numbers only in the spaces that do have part of the diagonal lines running through them .
This is the finished diagram !