The SUM formula can be applied to a certain number or cells or an indefinite series such as an entire column of data, which may grow or shrink at a later time.

When you type a seven-or-ten-digit phone number into an Excel cell that uses the phone number format, Excel will automatically change the way the number looks so that it appears as a phone number.

You can sum cells across multiple sheets in Excel. This article presents steps for Adding single-cell values or Adding values in the range of cells.