Average speed is not the average of two readings.
Entering at 60 and leaving at 80 does not necessarily mean an average of 70. Start with distance and time.
Divide distance by elapsed time
Average speed = total distance / total time. Use kilometres and hours to get km/h. For example, 10 kilometres in 10 minutes gives 10 ÷ (10/60) = 60 km/h.
These numbers illustrate the calculation, not a limit on a particular road. Covering the same 10 kilometres in 12 minutes gives an average of 50 km/h.
Why the numbers differ
Instantaneous speed describes your movement now. The average considers the distance and time since entering the zone. Current speed can drop quickly when you ease off the accelerator, while the average changes more gradually.
Taking the arithmetic mean of the entry and exit readings leaves out everything between them. Dividing total distance by total time is the general calculation.
What ALMET shows
ALMET displays its calculated average and remaining distance during a zone. This uses phone location data and is not an official measurement. Do not substitute the estimate for the posted limit.