Just noticed ScanGauge II records about 1% fewer miles traveled than the MFD. For example 314 vs. 318 miles since last fill up.
The Scangauge can be calibrated for tire size. From the Manual: "MORE>SETUP>SPEED Both speed and distance can be adjusted to compensate for changes in tire size, gears, tire wear, etc.. The setting can be changed at any time. If SAVE is not used, the entered value will be lost when the ScanGaugeII is disconnected. This may be the desired operation if the vehicle is not to have the ScanGaugeII regularly used on it." JeffD