The only way I have been able to tell is for some reason, the mileage goes down like . 2 in one day when you havent changed the style. . then the next day it goes back up.
I drive 13 miles each way to work. . 10 of it freeway. . I notice during the week, it will creep up a 1/10th at a time then one day it will drop . 2-. 3 ... then the next day it is back past that drop and up a 1/10th..... not changing style or habit. . this is what it does so I think that is the only way other than a pyro in the exhaust stream and read the 1200* temp while cruising. .