I learned how to make the arrowhead blocks yesterday at guild. You start with two squares, mine are 8" square, right sides together and sew around the outside leaving a couple of openings.
The little red plastic square is the marker we got so we didn't have to measure with a ruler on every pair where to leave the openings when sewing.
Then we made three cuts to each pair and sewed the pieces back together to form the block.
It's pretty cool! The interesting thing is that I started with 8" squares and these blocks measure 9", unfinished. Even though I understand the mathematics of why this happens, it is still strange. The instructions for this block and many others can be found in the book Rotary Cutting Revolution by Anita Grossman Solomon.
I only completed the two blocks shown in the previous picture above yesterday. I visited the rest of the time. Then the family went to the 5 pm showing of Harry Potter, because I decided I couldn't wait one more day to see it. Now I feel the urge to reread all the books.