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SubjectRe: W1: w1_slave units, standardize 1C or .001C? Break API
David Fries wrote:
> On Mon, Jan 21, 2008 at 07:11:07PM -0800, H. Peter Anvin wrote:
>> H. Peter Anvin wrote:
>>> Millikelvins would have the nice property of never being negative. :)
>
> True, but the sensor returns the value as a signed integer in C. That
> is where the earlier negative number problem was, it would have to do
> yet another conversion to go to Kelvin, and it would be just one more
> potential for error. Everyone knows that a bad conversion doomed at
> least one space craft, let's stick to Centigrade.
>

Uhm... the conversion is exact as long as you have at least centikelvin
precision (0 °C = 273.15 K by definition, and the multiplier is 1.)

>> Alternatively, centikelvins would fit nicely in 16 bits if anyone cares...
>>
>> 655.35 K = 382.20 °C = 719.96 °F
>
> The range for the sensor is -55 to 125 C, if an application didn't
> care about precision they could store it in a signed 8 bit value just
> fine.

This was more a comment as to it possibly being a convenient format for
more than this particular sensor.

The nice thing with kelvins is no need to worry about negative numbers
and something misparsing them, that's all.

I certainly did not imply that we should even consider use °F. That's
obviously ridiculous.

-hpa

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