display for a lookup

Hello guys,I wrote a lookup for my field.lookup has 2 values( description and value)How can I show the description on form by display?when I select value ,decription must fill to on form,but I just wantto show the desc field by display method on form

Write a display method on table and add it to the form.
See, \Data Dictionary\Tables\PurchLine\Methods\itemName

thank you again kranthi,I tried to add on modifield code vut it was unnessary.Thanks alot