These are not affected by system time changes, so time interval can be calculated even if the system time is changed by NTP or the user. That's why I can't use any function based on system time.
properly configured Unix NTP doesn't step-change the clock, it very gently slows it down or speeds it up until it is accurate and maintains stability. and only root can change the clock on a Unix system, so this really shouldn't be a concern.
-- john r pierce N 37, W 122 santa cruz ca mid-left coast
