[AccessD] Pass, Fail or Null

I have a subform that can have an infinite number of records.  On each
line is a result of that record.  If the test has not been performed,
the result is null.  If it has been performed, it can either be a pass
or fail.  If the record has 20 passes and one fail, then the entire
record is a fail.  However, the tests instances are entered in, awaiting
the test to be run, so the test result is null until the values are
filled in.  I am trying to pull an overall result in the main form.  If
all test results are null, or some are null and some are pass, then the
main form value would be null until all tests are run.  My brain is not
wrapping around this one - the nulls are throwing me.  Ideas?

Karen S. Nicholson
Programmer Analyst
EG&G Technical Services, Inc.
Pittsburgh, PA
Phone: 412-386-6649
Email: cyx5 at cdc.gov