Precisely accurate and correct time and date stamps are key to assuring integrity of the data and results output by each computerized system when validating spectrometry software. Topics covered are: working in an electronic environment, importance of accurate time and date stamps, the important of third party evaluation when a computer is used, 21 CFR 11 and Food and Drug Administration (FDA) guidance documents, FDA guidance on time stamps, matters of time and date stamps, time and date stamp formats, and validation issues for time and date. An audit trail output by software can only be reliable when time and date stamps are accurate. Without such, it is impossible to link a time and date stamp to any electronic record, or to build up a logical event sequence, or to establish the integrity of records and actions. ISO Standard 17799 on Information Management Security in section 9.7.3 for clock synchronization states that a computer or communications device with the ability to operate a real-time clock should have the clock set to a an agreed standard, such as Universal or local standard time. Because some clocks drift with time, a procedure should be in place to check for and correct any significant variation. FDA's 2001 Guidance states that systems have to be imported with a clear understanding of where the time stamp is located, and in 2003, the Part 11 Scope and Application guidance, the FDA urged that time stamps be imported with a clear understanding of the time zone reference used.