Question: I would like to know what the default settings for OS X are in terms of keeping the clock adjusted when I enable automatic time sync in the Date & Time preference.

I do know that the venerable `ntpd` daemon on Mavericks (10.9) and Yosemite (10.10) is no longer responsible for adjusting the time and instead a new program `pacemaker` has been introduced — so how can I know things are working or need adjustment to keep time?

Answer: 
To get a reliable answer on how well your clock is set, run ntpdate in debug mode:

```
ntpdate -d pool.ntp.org

```

This will gyrate for a while and end in a line such as

```
 1 Apr 17:38:16 ntpdate[4711]: adjust time server 123.45.67.89 offset 0.000810 sec

```

In this case, this meant to say my local clock was off some 810 µs (which would be spectacular, if actually true, but the value well below 100 ms does indicate a working synchronization).
To check clock sync, similar to the answer which suggests to run `ntpdate` in debug mode, you can also run it in Query mode for less verbose output.

```
$ ntpdate -q pool.ntp.org
server 85.199.214.102, stratum 1, offset 0.006256, delay 0.05470
server 95.215.175.2, stratum 3, offset 0.005234, delay 0.05624
server 217.114.59.3, stratum 2, offset 0.007166, delay 0.06274
server 85.199.214.100, stratum 1, offset 0.006319, delay 0.05396
22 Jun 09:20:55 ntpdate[84112]: adjust time server 85.199.214.100 offset 0.006319 sec
$

```

This is from my Mac running High Sierra 10.13.2, which runs `timed` rather than the NTP daemon (`ntpdate` still works because it doesn't use the NTP daemon).