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It has been written:
>	   [...]
>
>      The reason this is relevant is the typical meter is calibrated
>      assuming a straight line behavior (linear).  The two points that
>      determine this line are by default 0% O2 and whatever you calibrate
>      at. Most meters are calibrated at no voltage = 0% O2 which is wrong
>      according to these guys (two PhDs in physics and engineering between
>      them).  This zero reading is handy because people expect to see that
>      when there is no sensor plugged into the meter or the sensor is dead
>      and it also removes a difficult calibration step required for
>      accuracy.
> 
>      The troublesome step required for accuracy is correctly determining the
>      voltage that should be interpreted for 0% O2 for each individual
>      sensor.  For those of you that know your linear algebra this is the y
>      intercept, b, in the y = mX + b formula.  Y being voltage, X the % O2,
>      and m the slope or ratio of voltage to % O2.  Note that the % O2 is
>      based on the partial pressure of oxygen.  Crank up the gas flow and
>      pressure, and you'll see a higher O2 than is really there.

Please note that I know nothing about the specifics of O2 sensors, but
it seems suspicious to me that a sensor would be perfectly linear
between 0% and 100% O2.  It seems much more likely that in the middle
of the scale (oh, say from 30% to 70%) it may be close to linear, but
at the extremes (anywhere close to 0% and 100%) a sensor wouldn't
necessarily be close to linear.  I'd suspect something more like a
3rd order polynomial:

    |                                                                         
    |                .....                                                    
    |            ....                                                         
    |           .                                                             
    |          .                                                              
 mV |         .                   (excuse the cheezy ascii graphics)        
    |        .                                                                
    |    ....                                                                 
    |....                                                                     
    +-----------------------                 
    0%                     100%               
                                                                              

I don't know if I'm right or not, but it seems suspcious that a sensor
would give a strictly linear result.  Anybody _really_ know?

>	   [...]
> 
>      Got all that?  Let me know politely if something doesn't check here.

You've got to be kidding... politely?  :)
-- 
"What?  No Geek Code!"

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