If you make a mistake while entering a formula, hold down the Ctrl key and press Z. This reverses the effect of the last (undo-able) command.
Other commands to help modify formulas include the following:
• Click the delete button () on the Formula Editor keypad to remove the selected expression.
• Use the cut, copy, and paste keyboard shortcut commands or right-click a highlighted part of the formula and select Cut, Copy, or Paste from the menu.
• Drag portions of the formula to rearrange them.