Step 1- cut the rectangle or sashing strip to size
Step 2- if the pattern calls for cutting a 2-1/2"block and sewing on the diagonal-
INSTEAD--- use the EAR to measure what the block would cover.
This strip is 2-1/2 " wide, and the ruler is on the 2-1/2" mark.
Cut off the piece. (see next photo)
Step 3--- cut the corner piece from the next color 2-1/2" strip.
See how perfectly the pieces line up?
Sew with 1/4" seam, and finger press open.
For the next star point, cut another 2-1/2" corner piece from the next color 2-1/2" strip.
The dog ear will overhang. I like to cut it off before I sew.
Sew with 1/4" seam, check for accuracy, then trim underneath. (Save the trimmed piece for another project)
Here are your perfect double star points, no trimming, ready to go in your quilt.