A Grill for Secret Writing
A grill consists of a square of paper in which square holes have been cut in a certain way. Suppose that the paper consists of a square with four smaller squares cut off. Place the square on a piece of paper and write the first four letters of some text in the holes. Then, turn the grill a quarter turn and write the next four letters. Continue the procedure for two more turns.
 H. Lysing (J. L. Nanovic), Secret Writing: An Introduction to Cryptograms, Ciphers, and Codes, New York: Dover Publications, 1974, pp. 36–37.