title: Determine NTP-regulated system clock accuracy
body: <p>I can query a local NTP daemon using <code>ntpq</code> to get the system variables. For example:</p>
  
  <pre><code>$ ntpq -c rv          
  associd=0 status=0615 leap_none, sync_ntp, 1 event, clock_sync,
  version="ntpd 4.2.6p5@1.2349 Fri Nov  7 20:40:06 UTC 2014 (1)",
  processor="armv7l", system="Linux/4.5.0-00348-g4c53e80", leap=00,
  stratum=3, precision=-19, rootdelay=12.456, rootdisp=63.660,
  refid=195.219.205.9,
  reftime=dd9b0a27.3e1d46de  Wed, Oct 25 2017 13:03:35.242,
  clock=dd9b0da9.5274cdfc  Wed, Oct 25 2017 13:18:33.322, peer=14326,
  tc=10, mintc=3, offset=6.178, frequency=29.679, sys_jitter=0.409,
  clk_jitter=1.189, clk_wander=0.154
  </code></pre>
  
  <p>I would like to determine how accurate the system time is (relative to the root clock(s)). That is, what is the error window? For example is it given by the <code>offset</code> = 6.178 => accuracy +/-6.178 ms, or does offset mean something else?</p>
  
  <p>There are many other NTP questions that appear to touch on this subject but none seem to tackle exactly this question.</p>
  
  <p>UPDATE</p>
  
  <p>In the absence of any answers, and having read a variety of commentaries including that referenced by user3788685, I am no nearer the truth.</p>
  
  <p>One possible interpretation is that the root dispersion is the best measure, suggesting in the example above an accuracy of ±63.7 ms. Another suggests the offset (+6.2 ms). It is clear from external observations that the actual accuracy is certainly much better than 64 ms but I do not have the tools to hand to test it more accurately.</p>