W2002Intro101 - page 34 of 36

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D. Graphing

In many of your experiment you will use graphs to analyze and interpret your data. In order to

obtain meaningful result you will need to use a few basic principles, which are described below.

All graphs must be done of 1 mm grid graph paper found at the back of the manual.

Provide a title at the top of the page giving enough information so that it is clear what is being

graphed. The title should state the dependent variable vs. the independent variable.

Label each axis clearly including the units and magnitude. The independent variable

(experimentally varied quantity) is plotted on the x-axis (horizontal axis) and the dependent

variable (measured quantity) is plotted on the y-axis (vertical axis)

Examine the data to determine the scale for each axis. Choose a scale such that the

maximum area of the graph paper is covered and the point are easy to plot ( you may need

to rotate the paper 90

). The scale should also reflect the precision of the data plotted. For

example, if E

is recorded to 3 decimal places you should be able to plot it that precicely.

Note that the scale for each axis can be different and they do not need to start at zero

if it is not convenient

Carefully plot all data points using small dots in the correct position. The point should be

circled to make them more visible. (except for pH curves)

Examine the graph. If it appears to be linear use a ruler to draw a best fit straight line

through as many points a possible making sure that the points that lie above the line balance

those that are below. If any points appear to be way off the line neglect them and mark with

a question mark (?). If the graph is a curve draw a smooth line curve through all the points.