Puzzles - Missing letters puzzles

Starting at the top and working down, letters move through the alphabet in steps of 8 letters, then 9, then 10 etc.

Split the diagram in half horizontally and vertically. Start in the top left square of each quarter, and move clockwise around the other squares in the quarter. In each quarter, letters advance through the alphabet in steps of 2 for the upper left quarter, 3 for the upper right, 4 for the lower right and 5 for the lower left.

Start with the D on the outer left of the diagram, and move clockwise around the outer segments, then start on the N anti-clockwise around the inner segments. Letters advance through the alphabet in steps of 3, then 4, 5, and 6, repeating this sequence.