From: jimiii@nimbus.com (Jim Warford)
Subject: Re: electronic odometers (was: Used BMW Question ..... ???)
Reply-To: jimiii@nimbus.com (Jim Warford)
Organization: Nimbus Technology, Santa Clara, CA USA
Lines: 32

In article <13269@news.duke.edu> klg@mookie.mc.duke.edu (Kim Greer) writes:
>
>  I was wondering if anyone can shed any light on just how it is that these
>electronic odometers remember the total elapsed mileage?  What kind of
>memory is stable/reliable enough, non-volatile enough and independent enough
>(of outside battery power) to last say, 10 years or more, in the life of a
>vehicle?  I'm amazed that anything like this could be expected to work for
>this length of time (especially in light of all the gizmos I work with that
>are doing good to work for 2 months without breaking down somehow).
>
MK48T02 from thomsom.  It has a timekeeper (clock) and 512 bytes of NVRAM which
has a lithium battery backup.  The battery has a life of ~10 years of poweroff
operation.  Installed in a car it could be left powered on continuously and not
draw much current.  The battery would only be used when your auto battery was
dead or had been removed.

>Side question:  how about the legal ramifications of selling a used car with
>a replaced odometer that starts over at 0 miles, after say 100/200/300K
>actual miles.  Looks like fraud would be fairly easy - for the price of a
>new odometer, you can say it has however many miles you want to tell the
>buyer it has.

In California they have a line on the transfer of ownership form which states
that the odometer mileage is correct.  If incorrect you are required to 
fill in what you know (or guesstimate) to be the correct mileage.  If you
lie on this form and are caught you can be prosecuted and the buyer can
sue you for the value of the mileage differential.
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