This section is from the "Embroidery Stitches" book, by M. E. Wilkinson. Amazon: Embroidery Stitches.
Cross Stitch. A stitch adapted for working on canvas or coarse linen. It has three forms :- (a) Half-cross stitch ; (b) Whole-cross stitch ; (c) Double-cross stitch. The whole stitch forms a perfect square. The crossings must be uniform, i.e., the top halves must all slant in the same direction, likewise the bottom halves. Double-cross stitch must be worked over an uneven number of threads to allow a space for the horizontal central cross, as in (c).
(a)

(b)

(c)

 
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