Look for all data entry screens which contain dates and all reports and other outputs. An example is that many GPS units store dates in a nine bit binary number which counts number of days since Jan. 6, 1980. It will exceed the size of the counter on August 21-22, 1999. Some programmers knew that years divisible by 100 are not leap years, but didn't realize that years divisible by 400 are leap years. It also should recognize that 2001 and 2100 are not leap years.
Programs sometimes calculate future dates from the system's current date.
Dates are used to calculate number of working days, expiration dates, compound interest, due dates, leasing periods and various other Attachment 2-1 events. Current date is often used to establish an edit window for validating a date entered into the system. Note any calculations or edits using dates. Random number generators sometimes use current date as part of the formula. Since multiplication or division by 00 may cause the system to perform unpredictably, note any random number generators or other algorithms that may multiply or divide by the date.