Saddle stitch (flat stitch) method

Insert the needle through the first hole and align the threads on the front and back sides so that they are the same length.
Insert the needle into the next hole from the front and pull the thread in the direction of the sharp corner of the rhombus, opposite to the direction of travel, so that the needle does not pass through the thread.
Thread the back needle so that the thread does not cross over, then pull the thread from both sides of the front and back to tension the thread so that the seam does not float.
(*When threading from the back needle, proceed sewing so that the thread threaded from the front crosses the thread thread threaded from the back.)
(*If threading from the back needle, threading from the front should cross over the thread thread threaded from the back.) If tension is applied evenly each time when tightening the seam, the seam will be finished neatly.