On your piece of paper, draw two diagonal lines from corner to corner. Cut along the diagonal lines, leaving 3 cm uncut towards the centre of the paper.
You will have created four sections. Use the hole punch to create a hole in the top left hand corner of each section.
Fold the holes to the centre of the paper and secure with a pin. Pierce the pin into the straw or dowel. Take the pinwheel outside to roughly measure wind direction and speed.