The values present in the different textboxes can be
computed and the result can be shown to a target field
which has to be also a textbox.
  
The steps for this method are as follows :
  
1> Place some computable fields ie. Text Fields on the screen.
  
2> Open the property window of each of the Text Field and
change the datatype to "Numeric",which can be selected
from the drop down box of Data Type.
  
3> Place a button on the screen, on the click of which
the computation will take place.
  
4> Open the property window of the button and change the
Type to "None", which can be selected from the Drop down
box of Type.
  
5> On changing the Type of the button to "None",the Computed
Field button gets enabled.
  
6> Select "Yes" for the computed field.On selecting "Yes",
the "Expression" button gets enabled.
  
7> Clicking on "Expression" button a computed field setup
window comes on the screen.
  
8> Select the target field from the drop down box provided,
which contains the names of the textboxes having the
property,set to accept only numeric values.
  
9> Select the computable fields from the dropdown box provided
which also contains the names of the textboxes having the
property set to accept only numeric values.
  
10> After selecting each computable field an operator has to
be selected, which will show, what computation has to be
done between the selected computable fields.
  
11> After writing the required expression press "ok" button
to save the changes.
  
12> Press "Exit" button to return back to the property
window of the button.
  
13> Press "OK" button of the property window to return
back to the OCM wizard.