Quote Originally Posted by CA Jack
The old man didn't like mills as well, for several reasons, one of which was (as you mention in your second paragraph) feeling the dog's strength is impossible on a mill. How a dog walks, how hard it pulls, its alertness (or staleness) all these things not only can be seen better walking the dog, but felt better via the connection between him and you through a leash on a walk.
He is correct in that you can't feel that on the mill. When I'm using either mill for that process, I always make sure I walk the dog before he is to use the mill. That way I'm able to gauge his strength (along with the other things mentioned), or possible lack thereof, to make a determination on whether I've hit that particular spot or not. The mill is only a way to speed up the process of determining the weight.