**Introducing the first protractors scaled in radian measure!**

ProRadian protractors simply help you understand radians better. Radian measure is a fundamental concept in geometry, trigonometry, calculus, and physics – yet most students, and too many teachers, do not understand it. These new protractors let you learn about radians in the same way you learned about degrees – by measuring.

One radian is defined as the measure of the central angle when the length of the arc it intercepts is equal to the radius of the circle. If we unrolled a circle, one radian at a time, we would get a segment that was a bit more than six times the radius of the circle, like this:

In fact, it’s about 6.28 or exactly 2π times the radius. ProRadian Protractors are semicircles, so ProRadian 1, scaled in 0.1 radians, can measure approximately 3.14 radians, and ProRadian 2, scaled in π/24 radians, can measure π radians. The ProRadian Learning Set contains both protractors which allows you to make connections to the decimal form, like the output of your calculator in radian mode, and to the parts of π that you’ll use in trigonometry and calculus.

Starting to measure with radians in Geometry means that you will have one of the big hurdles in Trigonometry conquered. Besides, things like the patterns of numbers you find in regular polygons are really cool in terms of π.

ProRadian Pro is scaled in 0.01 radians, making it a precise measurement tool for work or school. It was made at the request of an engineer who bought ProRadian 1 but wanted a finer scale for measuring.

Please explore the site to learn more about ProRadian protractors and how to use them to build understanding of radian measure. Then visit the ProShop to purchase protractors for yourself or a Classroom Exploration Set for your class or to get information on submitting a P.O. Thanks!

Jennifer Silverman

jen@proradian.net