Hi
The trick is to start with the Month abbreviations before inserting your chart.
Start with your Month column. Enter Jan and then Feb. Select both Jan and Feb and drag down and Excel will automatically fill in the rest of the months for you.

While the selected cell is in your data range, when you use the Insert tab of the Ribbon and choose a chart type, Excel will automatically use the months as the x-axis.

You are correct that Hans is using a different version of Excel. While a chart is selected, the same features are available on the Chart Design tab of the Ribbon when you click the Select Data button. The dialog layout is a little different from Han's screen shot, but all the same functionality is there. Click the Switch Rows and Columns The Select Data Source button no longer requires a separate dialog and operates within a single dialog.

The old dialog that Hans showed is still referenced in the Excel Object model, but it is grayed out and the dialog itself has been removed from Excel for Mac. You don't need the dialog, but I thought you might want to know its history.
