title: Synchronize time in javascript with a good precision (>0.5s) (NTP-like)
body: <p>I'm looking for a way to synchronize time between clients with a good precision (let's say 0.5 seconds at least).</p>
  
  <p>I exclude using jsontime or exploiting timestamp in server response headers due to a poor precision (a second or maybe less).</p>
  
  <p>UPDATE:
  It should work even with mobile connections. It's not unfrequent (e.g. here in Italy) that 3G connections itself have a round trip time around 0.5s, so algorithm has to be robust.</p>