How does my device report speed?

Question: I noticed three different speed values on my report (Max, Avg, and Inst). How are each of those calculated, and why doesn't the system use the vehicle speed from my engine's computer if diagnostics are supported? Speed Definitions GPS Insight calculates speed using point to point GPS measurement, which is done by analyzing the straight-line distance traversed by the vehicle between two geographic points and dividing this by the time traveled to get the mph of the vehicle: Average speed. The average speed during a device’s report interval, which is obtained at the device level and then verified by calculating the distance traveled (beginning and ending odometer values) and time (update period). Instantaneous speed. The last speed value sampled during a device’s report interval. For example, if a device’s report interval is 2 minutes, the Instantaneous speed is the last data point obtained of the 480 data points collected…