[time-nuts] Can Lady Heather set PC time directly from aTrimbleThunderbolt?

John Hawkinson jhawk at MIT.EDU
Fri Aug 4 13:46:35 EDT 2017

David J Taylor via time-nuts <time-nuts at febo.com> wrote on Fri,  4 Aug 2017
at 17:18:12 +0100 in <90765FA83DAC4C7EAA06F9A781AA5906 at Alta>:

> BTW: you refer to "GPS time".  Not my area of expertise, but GPS
> time and UTC aren't the same - GPS time doesn't use leap-seconds,
> for example, so it's many seconds off from NTP.

We've been though this before, but I'll say it again.
This is not a very helpful thing to say.

"GPS time" is a very bad phrase to use, because it can mean "UTC derived via GPS," which is what most people mean. This accounts for leap seconds as most people expect. It is what essentially all consumer GPS receivers will display. 

But "GPS time" can also mean "GPS system time," the internal time used by the GPS system that does not include leap seconds. It is extremely rare that anybody means this, but it does happen (esp. on time-nus). And many GPS receivers can be convinced to display GPS system time.

So, please don't say "GPS time," because it is ambiguous. But please also don't suggest that when people say "GPS time" they must mean "GPS system time," because they rarely do and it's just an unnecessary bit of confusion.

--jhawk at mit.edu
  John Hawkinson

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