On Fri 10 Aug 2018 at 11:32:35 (-0400), Michael Stone wrote: > On Fri, Aug 10, 2018 at 10:18:19AM -0500, David Wright wrote: > >Currently we have a consumer radio clock which is a source of mystery > >to me twice a year: the DST change occurs in the early evening on > >Saturday instead of Sunday morning. > > The clock isn't properly decoding the DST bits. See > https://en.wikipedia.org/wiki/WWVB […] > Your clock is probably only looking at the first bit, and skipping > the logic for when to actually apply the change. A lot of the > functionality in the time code actually allows for relatively > graceful degradation like this to facilitate simpler or more complex > receivers.
Ah, that makes sense. So the different time of the change (which meant I didn't remember precisely what time it happened) is because of the varying offset (5, 6 hours) in spring and autumn, and a delay after that hour o'clock would likely indicate varying signal strength and lapses in reliable code detection. Now I know what's happening, I can watch for the latter. Being a dial clock, there's no signal strength indicator. Our LCD clock does display it approximately, but that only understands MSF, not WWVB, so it's now free-running (remarkably well especially since the Low Battery warning has been flashing since before Christmas). Cheers, David.
