Well recording "miles" on a trainer is rather bogus. I mean you can set the resistance really, really low and put it in your biggest gear have your little computer record your miles at tremendous average speeds but if you do you are fooling yourself.

Even being "honest" poses a problem. I mean, how does one know if you are going the equivilent of 17 mph or 20 mph or 23 mph?

About the best way to "calibrate" your wind trainer is to learn what your cruising speed is on a flat road with no wind at your average heart rate. You can get on the trainer and run that same heart rate in an hour do approximately the same thing. That is a way to put down your "mileage" on your training log.