It is important that when we have a graph we actually find it useful and can take information from it. First of all lets look at some misleading or badly-drawn graphs.
In the diagram above the scale on the left-hand-side graph is inappropriate. The numbers go up unnecessarily high on both axes which means the points are squashed into just a small part of the graph area. The scale on the right-hand-side graph is much more suitable. Because the scale suits the information the points fill the whole of the sheet making it clearer to read.
In the graph above the numbers on the bottom axis are unequal. This is wrong and makes the graph difficult to read.
Scales should either start at zero, or be concertinaed (squashed) as shown in the y-axis in the above graph.