This section is from the "Hand Sewing Lessons" book, by Sarah Ewell Krolik. Also available from Amazon: Hand Sewing Lessons: A Graded Course For Schools And For The Home.
Follow directions for Model 17 (Overhand Patch) to cut and prepare this model for patching. Baste the 4 inch square on the back to match and hem it to the opening.
Trim the patch to extend 3/4 inch beyond this hem, turn in 1/4 inch, baste, and hem it to the back of the model. When finished, the patch should extend 1/2 inch beyond the hemmed edge of the opening.