Keys that can be used in any mode
Numpad 1,3     decrease,increase     the distance between points drawn on the arc
key    R       randomize             the color of the arc
key    A       clear                 the screen
key    I       toggle clearing       on and off
key    1       select mode 1         for drawing an arc using a point , a radius , a starting angle and angle length
key    2       select mode 2         for drawing an arc from 2 points
key    3       select mode 3         for drawing an arc from point A through point B to point C
key    ESC     quit

Keys that can be used while in mode # 1
Numpad 4,6     decrease,increase     the starting angle of the arc
Numpad 7,9     decrease,increase     the angular length of the arc
Numpad -,+     decrease,increase     the radius of the circle
Arrow keys     move                  the center of the circle

Keys that can be used while in mode # 2
Key     H      reverse the handed-ness of the arc's curve (use the other circle's center point)

Left mouse click and drag the 2 different points that the arc is drawn between
Note : If it says that the arc is invalid , increase the radius with the Numpad + key

Keys that can be used while in mode # 3
Left mouse click and drag the 3 different points that the arc is drawn between
Note : If it says that the arc is invalid it is because all 3 points are on the same line
  or two are overlapping and have the same value