I break my charges down on an invoice so that my customers can see what is labor, design, set up, marking, thread, etc. I started doing this to help people get a better idea of the time and work that goes into the whole longarm quilting process. It probably works out about the same as when I was charging per square inch, but helps me to be more consistent in my rates. Somethings I charge by the hour, i.e. design, marking, unmarking...basically anything that happens before and after it's on the machine. I also give itemized estimates so my customers know what they can expect to pay. Hope this helps.