Graphing Techniques - Line Graphs

1. Calculate the scale to be used on the x-axis.
• The x-axis should be the independent or manipulated variable
• The ratio of the number of units in the data to the number of squares on the graph paper will yield the minimum number of units per square on the axis

600 g ÷ 50 squares = 12 g/square (minimum value)

• The ratio of the number of squares on the graph paper to the number of units in the data will yield the maximum number of squares per unit on the axis

30 squares ÷ 12 seconds = 2.5 squares/sec (maximum value)

2. Calculate the scale to be used on the y -axis.
• The y-axis should be the dependent or responding variable
• The ratio of the number of units in the data to the number of squares on the graph paper will yield the minimum units per square on the axis (see above example)
• The ratio of the number of squares on the graph paper to the number of units in the data will yield the maximum number of squares per unit (see above example)
3. Draw the x and y axis lines on your graph paper and mark off the scale
• Leave a margin of about an inch (4-5 squares on .5 cm grid paper)
• Do not number every grid line
• Mark each numbered grid line with a hachure mark
4. Label each axis with the quantity being graphed and the unit of measure
• Example: Mass (g)     or    Mass in grams
5. Plot the data points
6. Draw a best fit line
• DO NOT draw a line from dot to dot
• If a data point seems to be out of place, accept it as bad data and ignore it
• If the data points are in a straight line, draw the straight line that will leave about the same number of points above the line as below the line
• If the data points form a curve, draw a smooth curve that best fits the data points
7. Include a title for the graph
• The title should include both the independent and dependent variables
• The best wording is just like in the statement of the problem in an experiment
• Example: How does the depth of water in a lake effect the water temperature?