Circling / Compasses

We always need to make sure the radius of the circle on the ruler when we use the compass. It is not only troublesome and inefficient, but also inaccurate. This conception is based on the characteristics of isosceles triangle---the length of the median of two equal sides is half equal to the base’s. With the combination of compass and tape measure, you can assure the accuracy of radius quickly. When using it, you only need to the pull compasses, find the corresponding length, double it, and then you can get the radius of the circle (which can be corrected to millimeter), which will greatly facilitate the compasses operation.