The only thing to say about making it NOT easy to forget HOW TO DO THIS is:
Note: white sts are elongated for viewing in above how-tos. In working seam, tension sts to gauge of existing sts.
Step 1) Top red arrow: beg w/top piece, working right to left, insert needle around both sides of first st at end. (In TOP piece the whole st is always worked).
Step 2) Bottom red arrow: insert needle into center of first end st directly across from st worked in Step 1 and blue arrow on right: bring needle up thru the center of second full st to the left.
Step 3) Green arrows: in top piece insert needle around the next WHOLE st.
Step 4) Blue arrows: in bottom piece insert needle into center of the second st, then
up thru the center of the third full st to the left. (In BOTTOM piece 1 side of st in ea of 2 whole sts is always worked.)
Rep Steps 3 & 4 – complete across.
Step 5) Black arrows: insert beginning end of seaming yarn into center of first st on bottom piece (at point of red arrow).
Beginning with first stitch in both pieces, it’s always:
one whole from top – two halves from bottom
In the second photo showing part of an afghan, hexagonal motifs are joined with invisible seam to bring together the established pattern – Horizontal Garter St Invisible Join.
Swatches being joined in last photo are same pattern as in the afghan motif photo. Each motif ends with a garter ridge (two knit rows), then bind-off row is completed on right side. The same five steps of the invisible join method also used here … in each piece the row of flat sts worked is hidden between the bound off st and the garter ridge. Simply spread it out with finger tips and complete per instructions.
Later, the motif cross sts are completed individually by hand to match the cross sts of the established pattern.