I looked at this last night, and thought it was a great idea.
Then I thought about it in relation to the walk I did yesterday, when we walked for 5 hours on saturated rough ground, through heather and bogs and peat hags, lots of up and down though we never reached 1000 feet, quite a chunk of it against a biting wind. When I measured it on a map we had done less than 8 miles, though I was as tired as if I had done at least twice that.
I had visions of doing easy road walks at the end of the month to get my mileage up, even though I had expended far more than the required effort. Still, it might be a way of making me go out and do a mile or so on a day like today when it's blowing a gale, and I could curl up in front of the woodburner with my Xmas books. I'll have a think.