I'm a bit worried that I'm not keeping up with this, so I'd like to clarify some points for my own benefit: === The current time === - UTC/POSIX/CalenderTime are isomorphic, and represent some idealised notion of time where leap seconds don't exist i.e. a day always has duration 23:59:59. - Most (all?) system clocks return UTC. They may slow down around leap seconds to support this - is this behaviour only seen on systems with NTP? - It's not possible to simply get the number of actual ticks since some epoch; the OS time function may slow down for leap seconds and we can't avoid this. - This means TAI time can only be calculated accurately when we have the full leap second table available. === Durations === - Duration calculations are feasible for UTC at any point, as they're idealised. - Duration calculations are accurate for TAI only where we have the full leap second table, again. - Timing an event using the system timer where the event duration encompases a leap second will be inaccurate. - The duration between times A and B, where A->B encompass a leap second, will be different between UTC and TAI: UTC will not count the leap second, while TAI will include the leap second. - The duration between A and B, where both A & B are in the future (now + 6 months), will be the same in TAI and UTC because with TAI we won't know when the leap seconds are, so we assume and idealised calendar. Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************