Atomic Time

I want to tell you about a clock I bought a while back that my mate and I are very happy with. The La Crosse Technology WT-3102B 10-Inch Atomic Analog Clock.

It really isn't an atomic clock. It synchronizes with an atomic clock signal sent out by station WWVB near Boulder, Colorado. If you look at the signal strength maps you can see that the signal is the strongest in the night time hours. Which brings me to how to set up the clock.

At about ten minutes before the hour set the clock to 25 minutes before the hour and insert the battery. Your clock should be reasonably far away from electronic equipment. Especially TVs and Computers. Push the buttons as detailed in the instructions (you get the 4 American continental time zones plus a Daylight Savings on/off option). Then put your clock on an upstairs (no basements) wall that faces to or away from Boulder. When the clock gets the signal it will start spinning. You may have to wait until night to get a strong enough signal. If your building has metal sheathing (siding) the clock may only work in a window facing Boulder.

We put our clock up about 3 ft from a TV set (in a fairly strong signal area - your clock may need to be farther away) on a wall facing Boulder and have never been happier with a clock. We know what time it is to the second. And if the signal is never strong enough? The clock will work as a regular digital clock.

I have had older type atomic clocks that were much harder to set. This one is a piece of cake and I'm super happy to know what time it is. It is especially handy when daylight savings change days come as the clock adjusts automatically. No more clock fiddling to be on time.

Of course you still have to fiddle your alarm unless you have a Sony ICF-C318 Automatic Time Set Clock Radio with Dual Alarm (White). It really isn't an automatic set (WWVB radio) clock. It does adjust for daylight savings and it does have a built in back-up battery so you do not lose the time if the power goes off. The alarm itself is kind of soft, but the radio is loud enough to get you up and it is really obnoxious if you set the radio on top of a running computer. Setting the time and the alarm time are really easy with this radio. However the time does drift some (a few minutes a month). Which is why the atomic wall clock comes in handy.

Update: 31 July 2010 0300z

In the comments to this post rhhardin had a few complaints about a different model of this clock. I have not noticed any of the difficulties he mentioned. So either I was inattentive (possible) or the company fixed the problems in their later models.

Cross Posted at Power and Control

posted by Simon on 07.30.10 at 12:09 AM


Well, they may have improved it; but it looks a lot like mine.

I bought a dozen at discount in a grocery store and hung them in pairs.

They have an interesting bug when the time changes.

They change the hour at the appointed time, but at midnight GMT of the following day, they revert back to the old time. Then they set themselves right again at local midnight.

A computer programmer can figure out what happened pretty easily, a little flaw in the logic dealing with postponing the change to local midnight.

Anyway, the clocks are unreliable at time changes, bug or not; because you don't know if they got the DST bit, or got it right, that night.

Occasionally they're an hour off at random times of year.

When the battery is weak, some of mine shift time zones entirely. The minute is right, but the hour is wrong.

So, anyway, have a reliability indicating clock somewhere as well.

rhhardin   ·  July 30, 2010 5:31 AM

Where are you located? I live about 90 mi west of Chicago so the signal is fairly strong.

I would expect the troubles you are having are caused by a weak signal. A weak battery and a weak signal together and you are in for real trouble.

My guess is that in weak signal areas more frequent battery changes are in order.

M. Simon   ·  July 30, 2010 9:50 AM

The only problem with these clocks is that if you're running late you can't blame the clock!

Eric Scheie   ·  July 30, 2010 11:02 AM

I'm in Central Ohio. There's plenty of signal. Other atomic clocks have no problem.

It's a genuine firmware bug.

They do it twice a year, every year, in lockstep.

rhhardin   ·  July 30, 2010 1:28 PM


I was thinking more about erratic behavior at other times of the year.

M. Simon   ·  July 30, 2010 2:10 PM

They're pretty good usually. But they do depend on correct reception of the DST bit, and I think there is no parity check.

The time itself probably can be consistency checked, but the DST bit cannot.

My clock says Model WT-3101 on the back.

The couple that I've noticed with timezone changes are usually good. Just don't bet your life on it.

Battery low is indicated by 2-second clicks of the second hand, usually; and then the clock just stops.

rhhardin   ·  July 30, 2010 5:32 PM


For what it is worth this is a different model. Does it have a different movement? Time will tell.

M. Simon   ·  July 30, 2010 8:57 PM

I imagine they've fixed the daylight transition bug. It's likely why I got the clocks cheap at a supermarket, ie they dumped them.

Maybe not, though. Bear it in mind come Fall Back.

The DST bit problem is likely to remain, but is probably rare.

rhhardin   ·  July 30, 2010 9:08 PM


I didn't notice any of the symptoms you mentioned during the fall DST change. The clock set properly. I was not paying real close attention though. I'll be looking for evidence come this spring.

M. Simon   ·  July 30, 2010 9:45 PM

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