This app is about angles at the circle. The following terms and their properties are illustrated:

*Central angle*(angle at the center)*Inscribed angle*(angle at the circumference)*Angle between chord and tangent*

The central angle (blue) can be increased or decreased by using the slider. By dragging with pressed mouse button you can vary the vertex of the inscribed angle (red).

- Inscribed angles intercepting the same arc have the same measure.
- The measure of any inscribed angle is half the measure of the corresponding central angle.
- The angles between a chord and a tangent have the same meausure as an inscribed angle and half the measure of the central angle.