Sunspots

I was thinking of maybe doing a contunuation of my project from this year. My project this year was seeing if I could figure out how fast the sun is rotating by tracking sunspot movement over several days. I used proportions to figure it out and it was very close, within about three days. My Dad said that there was another way using trigonometry. I thought that I could gather lots more data and compare the two methods and see which is closer. Do you have any suggestions.