Graphs are vital tools for analyzing and displaying data. Graphs allow us to explore the relationship between two quantities -- an independent variable usually plotted on the x axis and a dependent variable usually plotted on the y-axis. Consider an experiment measuring the pressure of a gas while its temperature is varied. The measured pressure is the dependent variable, depending on the temperature set by the experimenter. In plotting a graph by hand, the key is to find a way to plot the two variables so that a straight line is obtained. If you use a computer, on the other hand, software can be used to fit data with a variety of functions. One purpose of this experiment is to compare how you graph by hand to how you can use a computer to help you graph. In general, you will face two types of situations: 
1) You have no theory relating the two variables. 
2) You have a theory that gives the functional relationship between the variables but the theory contains parameters you need to determine. 
In case 1, the relationship between variables can often be determined by investigating different types of graphs. In case 2, the slope and intercept(s) of the graph can be used to determine the values of parameters. 

How to draw a good graph 

 Keeping these points in mind will make for more effective graphs: 

1) Determine the minimum and maximum values of the data in both the x and the y directions.

2) Choose a scale for the tick marks on the two axes. Usually you will want to use as much of the graph paper as possible and make the scale on a given axis just sufficient to cover beyond the minimum and maximum values to be plotted. On the other hand, it's cover beyond the minimum and maximum values to be plotted. On the other hand, it's also best to use simple values for the tick marks. Some compromise between these objectives is usually necessary. 

3) Plot the data carefully (including error bars if applicable). It's often a good idea to plot the data as you take it instead of waiting until you finish collecting it. One of the lab partners may be able to record data in a table as well as plotting it while the data is coming in.