The Reference Timestamp is the time at which the server clock was last set or corrected. That does not tell anything about the local clock offset.

In order to guess the local clock offset an SNTP client has to evaluate four timestamps:

t1 = local clock, time request sent by client;
t2 = server clock, time request received by server;
t3 = server clock, time reply sent by server;
t4 = local clock, time reply received by client

The offset o is then calculated as:

o = ((t2 - t1) + (t3 - t4)) / 2

Net::NTP will save you the trouble of doing this explicitly and give you the offset right away. It will also not suffer additional inaccuracy from the delay between your gettimeofday() and get_ntp_response() calls.

In reply to Re: How to calculate the offset of your local time against an NTP reference server by martin
in thread How to calculate the offset of your local time against an NTP reference server by thanos1983

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