When you create a chart, Excel automatically fills in the axis with a range of numbers which many times will make the chart tougher to read. It will usually start the values at 0 even though you might need to start it higher. Below is an example.
It lists CPI rates by month. However the smallest is about 2.3% and the largest is 4%. However this chart starts at 0%. If we want to change that, you have to do the following:
Click on the chart and then click on the axis values, which is this case is the percentages. You should then see a box around them.
Click format under chart tools and then click Format selection on the far left.
This will bring up a dialog box. At the top of the first page are the minimum and maximum values. This is where you can change the values.
So now you should have a new chart that looks like this: