I need to track to retain the first value of a date field.  Each time
I load the worksheet the date field has the potential to change, I
need to keep track of the initial date in addition to the current date
that is in the field.

I have date columns called ASSIGNED and 1st ASSIGNED.  The initial
value of both will be blank.  At some point the ASSIGNED will be
populated with a date.  When it is populated for the first time I want
to save this value in the 1st ASSIGNED column.

I need something like:
  IF ( ISBLANK(ASSIGNED), "", ASSIGNED )
in my 1st Assigned cell, however, I do not want every value of
ASSIGNED.  I only want to update 1st Assigned if 1st Assigned does not
yet have a value.  I can't figure out how to put this kind of logic
together without creating a circular reference.

Can someone help?