How to add chart labels on your metric
First, expand the Date or Category (x-axis) section. Under Display, you will find options for the label size, unit, and location on the y-axis.
You also have the option to rotate the labels on the x-axis and to change the format (usually for dates).
Select a different data series as your chart labels
In Grow when you select your data series, Grow will automatically select the series title from the first row of the column.
You can rename this title to whatever you want.
Sometimes, your series labels are not present in the first row, but are present in the data.
Add Value Titles allows you to dynamically select the series titles from the data.
Your titles need to be sequential and in the same order as your data series.
Just click Display > then pick 'Add Value Titles' and select the cell or cells that you want.
The data series titles are displayed on the chart legend, as well as in the mouseover tool tip.