If Excel is not highlighting cells in the formula, enable 'Allow editing directly in cells' and 'Enable fill handle and cell drag-and-drop' in Excel options.

You can hide cell headings as well as the formula bar, and you can restore these labels to find hidden cell references as needed.

Learn how to show charts with hidden data cells in Excel. When there is data that is hidden in your table, Excel will not show that information in the chart.