Roll out a circle or an arc

Unroll the circle) to see how long its circumference is. Use the sliders to:
  • r: Change the radius
  • α: Unroll only an arc of the circle by changing the number of degrees to unroll
  • t: Manually control the unroll.
What is the exact length of the circumference of a circle of radius R=1? What is an approximate value to 2 decimal places? Why does it look like the grid is not square? What is an approximate value of ? Is the grid square 1:1? What is an approximate value for the length of the arc for 270° for a circle of radius R=1.5?