just checked ours, it compares 5 things:-
smooth driving (checks the driving isnt erratic)
road risk (checks the car isnt being driven on busy roads all the time with a higher risk of accidents happening, though how you avoid certain roads I don't know!)
time of day (doesnt like you driving too early or late in the day, again cant be helped if you have to do this)
length of journey(doesnt like little short journeys too much, which we do a lot!)
comparative speed (dont speed or at least dont drive too fast)
TBH dh and I drive relatively ok, we sometimes speed a bit say on 30MPH roads, like say 35 ish, but we dont drive like looneys, I just checked our results and it said we've done 1718 miles since the gps box was fitted and we've scored 74% so far, which must be acceptable as the insurance hasnt gone up. Our insurance for dh and myself was around £250 a year for us, adding ds1 to it made it go up by £500, he's 18, so we paid ours and half of his and its all worked out ok...so far!!!