Question : executing functions from update query

I have an function entered into a field in a table (Field is Field_Determination and one function is Mid(Description,1,3) ).  The question is: How do I get the function contained in the field to execute when a match is found in another table? I'm running an Update query

Answer : executing functions from update query

in a separate standard module you create a Public Function

Public Function TestExample(ExInput As String) As String
    TestExample = Mid(ExInput ,1,3)  
End Function

in a query ...

SELECT TestExample([MyField]) FROM MyTable

Steve