empty entry combo box

[skate]

I have a combobox for users to choose from the pull down, but occassionally they find they want to deleted their selection altogether (but not the entire record). Problem is I have an index field that is filled in depending on the selection, which is used later in another form and things get screwed up when the user deletes their entry but the corresponding "old" index number is not deleted.

 

[skate]

can't delete it manually b/c the users don't know what the index is for so I have to use code to automatically have it cleared.