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Old 10-09-2008, 04:37 PM   #6 (permalink)
cfg83
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Join Date: Dec 2007
Location: Southern California
Posts: 5,864

1999 Saturn SW2 - '99 Saturn SW2 Wagon
Team Saturn
90 day: 40.49 mpg (US)
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Hello -

I just did another GPS correction test :

Code:
              Car Odometer    GPS       GPS/ODO    % Correction
2007/06/19    19.00           19.6      1.0310     +3.1% (after purchased)
2007/06/19    36.15           37.2      1.0290     +2.9%
2007/12/01    30.40           31.2      1.0263     +2.6% (6 months later)
2007/12/05    31.40           32.3      1.0286     +2.9%
2008/10/08    34.1            35.1      1.0293     +2.9% (16 months later)
2008/10/09    35.6            36.5      1.0253     +2.5%
In the 2008/10/08 test, I wasn't being smart and did some strategic EOC, so I am sure that it contributed to the higher % (when you turn the key to the off position, the car odometer stops, but the GPS keeps right on chugging).

In the 2008/10/09 test, I was much more careful. I *like* that the % is going down over time. This is consistent with tread wear.

As stated before, I am sticking with a 2% error correction on my gaslog because I don't want to accidentally inflate (ha ha) my MPG numbers. Also, tire wear will eventually bring this correction down over time (i.e. always losing tread => always reducing tire circumference => always reducing odometer error over time).

Me happy, .

CarloSW2
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