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

Chuck Harris cfharris at erols.com
Tue Jun 30 11:25:03 EDT 2015


Hi Andy,

I think you would be guessing wrongly.

The vast majority of watch owners don't want to ever have to set,
wind, adjust the calendar, or in anyway think, or fiddle with
their watch's time.  They want it to just be right.  In other
words, their disinterest makes them the "anti-time-nut".

The engineering team that designed the watch is where the concerns
about the watch always being "right" get turned into hardware.  It
costs them only a few days of an engineer's time to put, a temperature
sensor, battery voltage sensor, and a table describing the nominal
performance of the crystal at a normal range of temperatures and
voltages, into the watch.  It costs nothing on a per watch basis,
as it is a trivial amount of additional silicon... silicon that
resides within the necessary spaces between the pads used to connect
the silicon die to the circuit board.

As to per unit testing, the only testing required (after the initial
design phase) is to program an offset into the watch that makes up
for minor frequency variations in the crystal at nominal room
temperature.  Crystal manufacture is an imperfect process, so they
have to do that anyway.

-Chuck Harris

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



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