Calculated control is blank due to control contains a Null value.
Cause:
The calculated control's Control Source expression refers to a field that contains a Null value. A Null value is treated as an unknown value rather than a zero. Any calculations performed on a Null value will return a Null result.
Solution:
Convert the Null value to 0 using the 'Nz' function. In the Form Design view, select the desired control, select the 'View' menu, and select 'Properties'. Select the 'Data' tab, and add the 'Nz' function to the Control Source expression.
1) If the Database window is not active, activate the Database window.
2) Click the 'Forms' tab in the Database window.
Forms tab
3) Select the desired form from the list box. (The selected form is highlighted.)
4) Click 'Design'. (The selected form and the floating Toolbox appear.)
5) Click to select the desired control. (Handles appear around the control.)
Handles appear around control
6) Select the 'View' menu and select 'Properties'. (The property sheet appears.)
7) Click the 'Data' tab.
Property sheet
8) Click in the 'Control Source' property box.
9) Build the expression using the Nz function in the 'Control Source' property box.
EXAMPLE: =Nz([Subtotal])+Nz([Quantity])
(where ([Unitprice]) and ([Quantity]) are fields that may contain Null values to be changed to 0.
10) To close the property sheet, click the 'X' in the upper-right hand corner of the property sheet.
Click X button to close property sheet
NOTE: The properties will be saved only when the design view is saved.
