Mileage difference in logs

[supersnoop]

I noticed some strange behavior in my log files. I reset my trip meter and logged 203 miles last weekend. But when I pulled my logs, it only showed 197 miles for the trip. This was a single key-turn journey with no stops, so there should Only be a single entry in the log file. Is this normal? Has anyone else noticed such a discrepancy? According to all my maps and experience, the trip meter is correct, not the log.

 

[slcasner]

Your third sentence contains an editing error, so I'm not sure exactly what you were saying about a single entry in the log file. I guess you are referring to the once-per-day record. If that occurred before the end of the trip, it might not contain the final value. There are also records every 10 minutes while the car is turned on that carry the odometer value. Between those records you can integrate the speed in the records emitted every second to get distance. I've never seen a discrepancy like 197 vs. 203.

 

[gregd]

I wonder if one measurement is from the odometer (counting wheel turns), and the other from the GPS (with its jitter factored in)? Was the trip pretty much straight line, or did it have a lot of curves and/or GPS-affecting tunnels or tree canopy?

 

[supersnoop]

It was a drive from Dallas to Austin, so mostly straight lines in wide-open spaces. I guess there a one-mile-long tunnel in Dallas, but no coverage other than that.