Seems unnecessarily complicated! Sure, it's important to keep an eye on number of sales, and sales per week, and a whole host of other things as well as total income... but the biggest question for me is "will the green dot on the far right be higher or lower than the green dot to the left of it?"
If it's the same at the end of the month, then you've had a 0% drop... if it's half, then you've had a 50% drop. But if it's half when you're only half way through the month, that's not a 50% drop. I appreciate that doesn't take number of sales into account, but if you're having a 50% drop in number of sales, but still earning the same amount of money... then it;s not all that bad. You can't pay your bills with 'number of sales' alone... it's the cold, hard, filthy cash that counts. And based on your chart, you're probably going to make around plus or minus 10% of what you did last month.