Plotting Points on a Graph
Key Concepts
Labelled Axes
The horizontal axis, the x axis, is used for the independent variable, that is, the variable which you control (set at several known intervals).
The independent variable is also sometimes referred to as the controlled variable.
The vertical axis, the y axis, is used for the dependent variable, the variable that you observe or measure when you change the independent variable.
Would you like to see what this means using an example? 
Click this link to go to the complete tutorial if you are an AUSeTUTE member. 
Not an AUSeTUTE Member?
 Find out how an AUSeTUTE Membership can help you here.
 Become an AUSeTUTE member here.

Units of measurement are written after the name of the quantity in the labels of each axis.
This can be done in several different ways:
 units in round brackets after the name:
example: time (min) and mass (g)
 units separated from name with a comma:
example: time, min and mass, g
 units separated from name using a forward slash:
example: time / min and mass / g
This is now the most acceptable format.
Each axis should be marked off in regular intervals, referred to as the scale.
 Horizontal axis:
eg, if you measure time every minute during the experiment, mark off 1 minute intervals on the x axis and label each mark as 1 then 2 etc.
A suitable scale might be to let 1 cm on the graph paper be equal to 1 minute.
 Vertical axis: inspect the values of the dependent variable then
(a) round up the highest value to a convenient number (eg, 14.12 g might become 15 g or even 20 g)
(b) round down the lowest value to a convenient number (eg, 2.92 g might become 2 g or even 0 g)
(c) calculate the range of values you need to plot
(ie, highest value minus smallest value, eg, 20  0 = 20)
(d) decide on a suitable scale: metric graph paper might have lighter ruled divisions every 2 mm and darker divisions to mark every 1 cm.
For a range of 20 g, every 1 cm on the graph paper could represent 1 g
You do not need to start either the x axis or the y axis at zero, unless zero has some special significance.
Title
The title of a graph is usually in the format of "yaxis label (without units) versus xaxis label (without units)".
The word "versus" is Latin for "against".
The first step in writing a title for the graph is to remove the units from the labels on the x and y axes:
 yaxis = mass
 xaxis = time
Then we construct the title of the graph in the format yaxis versus xaxis, that is, "mass versus time".
The word versus is often abbreviated to vs
Using this abbreviation, the title of the graph becomes "mass vs time"
If you are including more that one graph in your lab report, it is a good idea to number the graphs as well.
You can use the phrases Graph 1., Graph 2., etc
or you can use the more general phrases Figure 1., Figure 2., etc
When you refer to a graph in your lab report, you write, "Figure 1. Mass versus time".
When you are talking to someone about your graph, you might say, "Figure one, mass versus time", or you might say, "Figure one, mass against time".
Plotting Data Points
The data obtained from an experiment is plotted on the graph using a suitable symbol.
The symbol used must be large enough to be seen, but small enough so that there is no uncertainty about where the centre of the point is.
For this reason, the first choice for plotting points on a graph is a cross, x (the point is located where the two lines forming the x crossover, but, the two lines themselves make the point easy to see on the graph).
Would you like to see what this means using an example? 
Click this link to go to the complete tutorial if you are an AUSeTUTE member. 
Not an AUSeTUTE Member?
 Find out how an AUSeTUTE Membership can help you here.
 Become an AUSeTUTE member here.

If the points on the graph form the pattern of a straight line or a smooth curve, draw the line of best fit through the points.
The line will
 start at the x value of the first data point
 end at the x value of the last data point
If you need to include more than one set of data points on the same graph, use two different symbols, that is, use one symbol (x) for the first set of data but use a circle (o) for the second set of data points.
Would you like to see what this means using an example? 
Click this link to go to the complete tutorial if you are an AUSeTUTE member. 
Not an AUSeTUTE Member?
 Find out how an AUSeTUTE Membership can help you here.
 Become an AUSeTUTE member here.

