Hi welcome to 3FC
While a stone a monthly is most likely achievable, it's not something you can keep up month in and month out. They recommend losing 1-2 pounds a week ( obviously you lose quite a deal more in the first two weeks or so)
They also say that having less than 1200 calories a day (if your a women) is not such a neat idea, you're probably hindering your weight loss by going into "starvation mode" and slowing your metabolism.
If your serious about changing your life for the better, throw out the fad diets, research nutrition and fitness, work out a plan that suits you and give it 100%
You can do it, the weight loss may be slower but I guarantee it will be easier to keep off and maintain.
But if you are set on the diet you have chosen, I'm sure you will find everything you need to know in the "General diet plans and questions" you will reach a must larger audience in there.
Take care, good luck and be positive!