Well here is my informal data from the IAT sensor from ScanGauge compared to my Wayfinder Compass/Temperature Gauge.

In town during the day:
ScanGauge = 87 deg F Wayfinder = 79 deg F

On the highway during the day
ScanGauge = 77 deg F Wayfinder = 74 deg F

During Night at Grand Canyon
ScanGauge = 44 deg F Wayfinder = 42 deg F

Early Morning at the Grand Canyon
ScanGauge = 22 deg F Wayfinder = 23 deg F

Of course, the colder it was the better they seemed to correlate which seems to make sense. And there was no correlation sitting at idle as the IAT temp always was much higher!