Move the mouse inside a graphical sheet's viewport. You will see the arc center cross follow the mouse.
Mouse Center Point
Left-click when the center cross is where you want to start the arc or press the Enter key followed by the X value, Enter/Space/Tab, and then the Y value and Enter/Space/Tab.
You will next be prompted for the start angle of the arc. Moving the mouse defines the arc's diameter and displays the start angle. Left-click to define the start angle of the arc or press the Enter/Space/Tab key followed by the start angle numerical value in degrees.
Arc diameter and start angle
Now move the mouse to define the arc's end point . Finally left-click to define the arc or press the Enter/Space/Tab key followed by the end angle numerical value in degrees.