[time-nuts] Casio Watches 13 Year Drift in Seattle

Bob Camp kb8tq at n1k.org
Tue Jun 30 09:43:44 EDT 2015


> On Jun 29, 2015, at 6:03 PM, Andy <AI.egrps+tn at gmail.com> wrote:
>   "If this was normal back at the turn of the 20th century, why wouldn't
>    Casio, and others at least do as well?  Especially now that all
>    electronic watches have a microprocessor built in... complete with
>    temperature sensing diodes, battery monitors, and other nifty gadgets."
> I am guessing the vast majority of Casio owners don't especially care if
> their watch gains or loses a minute every month.  

Most don’t, but some do. The ones that do care talk a lot. When they go online
with a “this watch is junk” post (with lots of data) it impacts the market. 

> So why bother to add
> sensors and circuitry to compensate for its environment?
> Furthermore, it requires setting the initial frequency on each watch built,
> to compensate for the crystal's initial error.

That’s been done since the original quartz watch designs. It’s done with a robot
these days and is part of the checkout process on the module. It actually saves
money. The precision of the crystal (and other parts) used can be lower if you
do the calibration. Lower precision => better yield => lower cost. 

The chip in the watch likely goes into just about every watch they make. The
size of the die is dictated by their ability to dice the wafer (roughly 1 mm square). 
Anything smaller than that makes no sense. However many devices you can 
pack into that much area, you get for free. With a modern process, that’s a *lot*
of devices.

One might think that running a much older process would be cheaper. That would only
work if you made more watch chips (by wafer lots) than you make of everything else. 
That’s just not true. The answer is (as with everything else) that you keep up fairly
close to a modern process. The process parameters for an ultra low power watch
chip will be a bit different, but the geometry is dictated by the basic gear on the line. 
They all rumble down the same basic line at one of many (massively large) foundaries

>  And that jacks up the cost,
> perhaps more than adding those sensors would.  Better to just churn them
> out with as little per-unit testing as possible.

An accurate watch “with all the testing” sells for < $10. The market for an much
less accurate watch would (presumably) be at an even lower sell point…. 


> That's just my guess ... but who am I to say?
> Regards,
> Andy
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