Not sure why you would question "average speed".
Seems to me a straight forward calculation.
Now "calories burned" could be a different matter because of many more variables such as considering elevation change-time-speed considerations. After logging 22 rides with it (I log date, distance, max speed, ride time, max elevation & calories) I have found that the data seems reasonable & CONSISTANT from ride to ride).
I have no idea what kind of algorithm they use for calories but if it is important to you, drop them a line. They have been very responsive to some questions I had.