In the Insert Field dialog box, Field Category list, select Objects.
In Field Names, select Formula.
To enter a formula, do one of the following:
Select Average, Sum, or Count from the Type drop-down. The Insert Field dialog box closes temporarily. To specify a range, click inside the first and the last cell. The result is appended to the formula.
Click Cell. The Insert Field dialog box closes temporarily. Select a cell in a table in the drawing. The cell address is appended to the formula.
(Optional) Select a format and a decimal separator.
Click Choose.
To save your changes and exit the editor, press Esc until no cells are selected.