Graphs and Graphical Methods

Wherever possible, the data from an experiment should be plotted at an early stage, even if numerical methods will be used subsequently for greater accuracy. This is particularly tme when functions are to be fitted by least-squares or other methods, since a graph may make evident special problems or requirements that might otherwise be missed. 

In preparing final plots, whether computer generated or prepared by hand, there are several important features to consider. 

Use Clear Scale Labels. Choose suitable scale divisions with longer tick marks used for the major values along a scale that will be labeled with the appropriate numerical values. Under the scale numbers for the independent variable, enter the scale label, stating the quantity that is varying and its units e.g., 

Use Distinctive Symbols. If data have been taken on two distinct runs—say a series of measurements on heating and then on subsequent cooling or merely duplicate runs made with the same protocol—use different symbols to denote the separate runs. If approximate estimates of the uncertainty in the variables is available, then add error bars to each point. 

Distinguish Smooth Curves. If your plot contains several empirical smooth curves or several theoretical curves, it is wise to distinguish them by using dashed and dash-dot curves as well as solid lines. 

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