I'm not sure how I feel about the idea of the "stone" measurement. You sure have to lose a lot to be able to take "1" off of your weight. It doesn't seem like you get enough credit for each individual pound.
How tall are you? From your picture it looks like you've already hit your goal weight. If you weigh 300 then you carry it very well.
Good luck with your mini-goal. And don't make that walk too leisurely.