GRAPHINGAlgebraThe use of a graph starts with the plotting of data points using the coordinate system. These datapoints are known as the abscissa and the ordinate. The abscissa, also known as they-coordinate, is the distance along the y-axis. The ordinate, also known as the x-coordinate, isthe distance along the x-axis. A point on a Cartesian coordinate graph is specified by giving itsx-coordinate and its y-coordinate. Positive values of the x-coordinate are measured to the right,negative values to the left. Positive values of the y-coordinate are measured up, negative valuesdown. For example, the x- and y-coordinates are both zero at the origin. The origin is denotedas (0,0), where the first zero refers to the value of the x-coordinate. Point A in Figure 1 isdenoted as (0,4), since the value of the x-coordinate is zero, and the value of the y-coordinateis 4. In Quadrant I, every point has a positive x-coordinate and a positive y-coordinate. PointB in Figure 1 is located in Quadrant I and is denoted by (4,2). Fractional values of coordinatescan also be shown. Point C in Figure 1 is denoted by (1,1.5). In Quadrant II, every point hasa negative x-coordinate and a positive y-coordinate. Point D is denoted by (-2,2). In QuadrantIII, every point has a negative x-coordinate and a negative y-coordinate. Point E is located inQuadrant III and is denoted by (-2,-4). In Quadrant IV, every point has a positive x-coordinate,but a negative y-coordinate. Point F is located in Quadrant IV and is denoted by (5,-4).CartesianCoordinateGraphsThe most common type of graph using the Cartesian Coordinate System is one in which allvalues of both the x-coordinate and the y-coordinate are positive. This corresponds to QuadrantI of a Cartesian coordinate graph. The relationship between two physical quantities is oftenshown on this type of rectangular plot. The x-axis and the y-axis must first be labeled tocorrespond to one of the physical quantities. The units of measurement along each axis must alsobe established. For example, to show the relationship between reactor power level and time, thex-axis can be used for time in minutes and the y-axis for the reactor power level as a percentageof full power level. Data points are plotted using the associated values of the two physicalquantities.Example: The temperature of water flowing in a high pressure line was measured at regularintervals. Plot the following recorded data on a Cartesian coordinate graph.Time(min)Temperature(°F)0 400°15 420°30 440°45 460°60 480°75 497°90 497°105 497°120 497°MA-02 Page 74 Rev. 0