To buy, or not to buy

The book Geek Logik by Garth Sundem attempts to break down a number of every day decisions into mathematical equations. It's an interesting read, and as I like numbers, I thought I'd include his "Should I buy it" equation here. I take no credit for the actual equation, but hopefully this calculator will help you make a purchase desicion!

Should I buy it? Here is what infomation we need to work out this equation: WIN [ M(S - B - R) + £b ] = B 70 £i W How much do you want this thing? --- Please select between 1 and 10 --- 1 - I don't really want it 2 3 4 5 6 7 8 9 10 - I must have it! N How much do you need it? --- Please select between 1 and 10 --- 1 - I don't really need it 2 3 4 5 6 7 8 9 10 - It's absolutely essential I Is it a good investment? --- Please select between 1 and 10 --- 1 - No, it'll be worthless soon 2 3 4 5 6 7 8 9 10 - Best investent in the world! M How long have you wanted it? months (S - B - R) How much money do you have left at the end of each month? (Note that I've combined this from (S - B - R), which originally was (Salary - Bills - Rent) £ (Enter a negative figure if you always run out of money!) £b What is your current net worth in bank and credit cards? £ (Enter a negative figure if you're in debt) £i How much is the thing you want to buy? £