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General Graph Properties In most experiments you will be required to construct a graph. It is the lab instructor’s prerogative to allow you to use Excel or other software packages to construct your graphs. All graphs (manual and electronic) have the following properties: 1. A good graph fills the whole page. The data points should extend across as much of the page as possible. This implies that there should be only one graph per page. 2. A good graph has a title that describes what is being plotted. 3. A good graph has axis labels that describe what is being plotted on each axis. 4. A good graph has tick marks both major and minor to indicate the divisions of both the x and y axis. 5. A good graph has axis units describing the units represented by the tick marks. Acceptable axis units are those that clearly label each axis with correct units corresponding to the measured quantity plotted along the axis. For example, for the x-axis “2d [cm]” denotes that the quantity 2d is measured in cm and each major tick mark represents a multiple of centimeters scaled according to the graph page. 6. A good graph has evenly spaced tick marks, unless otherwise indicated by the lab instructor. 7. A good graph must clearly show the y-intercept plotted on the graph, that is, graph the point (x = 0, y = b), for b is the value of y when x = 0. Consequently, the continuity of the x and y axes must not be broken. Showing the yintercept may be easier if the x and y axes are placed inside the graph-paper lines. See the graph examples on pages 12 and 13. 8. On a good graph, the numerical values of the slope and y-intercept are clearly written. 9. A good graph has the points used to measure the slope clearly indicated. These should be points on the line and not data points. The points used for the slope calculation should be marked differently from the data points. Choose points on the line as far apart as possible.
