|Join two tumbling block units and press to one side.|
Unpick any stitches in the centre seam allowances.
|As before place third unit on the unpressed unit, pin and sew. Unpick.|
|Wrong side up and the final open seam away from you, bring|
seams two and three towards you so that the centre TB unit is
folded up between the side units.
|Pin, sew and unstitch.|
|Now you have three gaps and three obtuse units to insert.|
|Place obtuse diamond on the unpressed side . . .|
|Pin and sew past the edge, then unpick and turn wrong side up with unsewn seam away from you|
and fold, pin and stitch as before.