Showing gridlines is useful when you are displaying intricate values. Gridlines will show the value of a decimal place, whereas not showing the gridline will only give an approximation of the value. You can use the toggle buttons on the Chart toolbar to turn gridlines on or off for either axis.

 

Trendlines are similar; they are used to show a common trend in a diagram. You can display them on any chart except ones with 3-D effect.

To add a trendline, click the Chart menu and click Add Trendline. A dialog will then open where you can set your options: