I had the privilege of working with five motivated and thoughtful teachers this week who will be teaching our Geometry21 course this year. I had about six hours to show them what this course is all about and make them understand what blended learning looks and feels like. I think it will be a great year!

I also wanted to be sure they understood radian measure! So, naturally, I broke out the ProRadian Protractors, and they started measuring. I listened with great satisfaction when they found those first interior angle sums and said, “Ohhhhh.” I happily watched these new lightbulbs going off as we continued the lesson. I got to the part with my slick GeoGebra applet, and saw a definite hint of cloudiness coming over this previously clear thought. Thankfully, I also had a lightbulb moment!

I asked the teachers to find a strip of paper on the table (scraps from making pinwheels and Liu Hui blocks) and make a mark at one end. Then I had them place the zero of ProRadian 1 on the mark, and roll it along the strip. Every time an integer value “touched” the paper, they made another mark on the strip. In the end, they had a “ruler” whose scale equaled the radius of the protractor. Knowing that I could not be there to show this to every user, I made a much simpler GeoGebra applet.
Try it here!