The ride was from the north edge of Indy proper up to a small town about 20 miles north, and back home again.

I understand that the data can be affected by changes in barometric pressure, like when a front rolls through, but in both cases where this has happened there has been no change in the weather. I didn't even think, though, that temperature changes might affect it. The first time it happened, I was stopped for breakfast and the ambient temps might have increased 6-8 degrees F during the stop as the morning warmed up. This last time (the ride from which the graphs were taken), there was no change in the actual air temperature. Having said that, however, on both rides the unit was sitting in sun during the stops, and the temperature graphs show an instant increase in temperature while at the stop, followed by a gradual decline once I started riding again. So at least the temperature readings seem to be affected by sitting in the sun.