Is there anyone knowing "How to set up a default value of a field
based on the same field"?
Not sure what this means, but the answer is still, "You can't".
Default values are assigned to fields at a time before _any_ of them have
any values -- it's an empty record.
What you probably should be able to do is to use the AfterUpdate event of
some control on the form to calculate the value you want inserted in the
other one. Be aware, however, that this question often a cover up for a
likely Design Error, for example storing "redundant" data.
Hope that helps
Tim F
