You can show either Major or Minor or both types of Gridlines on a chart in Excel 2010. These three types of grid lines assist in scaling the chart against set parameters. If you’ve created one huge chart, you may need to insert gridlines for correctly measure every data point with it. To do so, select the chart and navigate to Chart Tools Layout tab, in Gridlines pull-down menu, from Primary Horizontal Gridlines options, select a desired type which you wan to insert.
Now from Gridlines options, select a Vertical Gridline type to insert gridlines at Y-axis.