track of where i send each letter, i.e. what zip code or town or state. then i can begin to see which letter pulls best for me. i then begin to use only that letter.
then you want to figure out your actual break even point. you know your advertising cost and you know what you can afford to get a lead. so you divide what you can afford to spend at break-even for a sale into your advertising cost. then you will know how many sales you must get to break even.
let's say your break-even or par is 5%. if you're not getting that you can do a number of 