ntpd not updating time

I had updated my old iMac to Mavericks just fine. I then bought a new (certified refurbished, actually) iMac and migrated everything over from a Time Machine backup. The new iMac's clock loses several seconds a day. When I unlock the *Date & Time* system preference, the time then synchronizes to the correct time immediately. But then it just loses time again. I read [this answer](https://apple.stackexchange.com/a/111859/30226) and now have a total of 3 time-servers, but it doesn't seem to solve my problem. In the system.log file, there are these relevant messages: Dec 3 22:31:34 iMac.local ntpd: SYNC state ignoring +0.155735 s Dec 3 22:31:35 iMac.local ntpd: ntpd: time set +0.308737 s Dec 3 22:31:35 iMac.local com.apple.time: Interval maximum value is 946100000 seconds (specified value: 9223372036854775807). The Interval maximum value one doesn't look good. Anybody know how to fix this so that the time stays sync'd? --- Update ====== It took a little while, but the addition of multiple time servers *did* make it better (not perfect, but better). Now it *gains* time, but seemingly at a much slower rate. If the addition of multiple servers (3 in total) had anything to do with making it better, perhaps (?) the addition of yet more servers will make it better still. I now have a total of 5 servers in ntp.conf. I'll watch it over the next couple of days and see what happens. (Even if this fixes it, this still doesn't answer *why* all of this is necessary to fix it in the first place. An answer to *that* would be nice, but I'll settle for it just being fixed at this point.) BTW: you *can* set multiple via the **System Preferences** GUI: just type server names into the field with commas to separate them. This keeps the GUI and the file in sync. BTW #2: [here's the site](http://support.ntp.org/bin/view/Servers/WebHome) I got the list of publicly accessible NTP servers from.