well row 24 has you binding off stitches in the middle dividing your work and leaving you with 10 stitches on either side.
im not 100% sure how you do the cast on, but adding in the extra strand meens you can use a long tail cast on when you already have stitche son the needle, ordinarilly you would have to use a knitted or backward loop.
once you have 20 stitches on your needle (10 knitted and 10 more cast on you work rows 26 to 28.
you will then have 10 stitches left on your needle which you havnt worked since row 24. You rejoin your yarn and work from row 25 again. this creates to distinct sides for the crossover straps.
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