There are various things that happen, but the main function is to test current and slightly back level software for compliance, and rate it according to our own Acceptability Index.
There is a fairly strict set of rules to determine whether a product is "compliant" or not.
Y2K Cinderella Acceptability Index 0 Good, 9 Bad 0. Fully Compliant, ISO/ANSI/FIPS, YYYYMMDD 1. Acceptable, cosmetic display problem hH:MM:SS,xx 2. Acceptable, 4 digit ambiguous, MMDDYYYY 4. Acceptable, 2 digit YMD, YYMMDD 6. Acceptable, 2 digit ambiguous, MMDDYY, DDMMYY 8. Borderline, garbled output 19:0/02/29 9. Unacceptable. Replace or else. (none found, to date.)(There is an apparent inconsistency here. Which the wide awake will have spotted. Why should a 4 digit ambigous date score better than a two digit nonambiguous year. Well 4 digits good, 2 digits bad is the tie breaker. 4 digits are still better even if they are in the wrong place. A logic does exist.)