Curves are represented in a planar coordinate system that you can think of as being like a piece of graph paper. Just like plotting points onto graph paper, the points that control the curve are defined by a horizontal and a vertical distance from an origin. The origin is located at the center of the ‘page’.
Normally you will use the mouse to position your points visually, but on occasions you may need to type in the coordinates. When typing in coordinates the distance is normally entered relative to the origin. The horizontal distance is entered first followed by the vertical distance.
If the point is to the right of the origin, then the horizontal coordinate is a positive value. If the point is to the left, then the value should be entered as a negative number with a minus sign (-) immediately in front of the number. Similarly for vertical coordinates where points above the origin are positive and below are negative.
As an example of this, if you were to draw four points forming the corner of a 100x100 square with the bottom left corner at the origin then the coordinates you type in would be as follows….
If you are using the mouse to enter points then there is a special way to display the 2D coordinates of any point on the screen. Press the Control key, and the current cursor position will be shown in the message lines. The cursor value changes continuously as you move the cursor.