Best bet is to do just what you already suggested. Get your machine out, dump a bag of candy into it and start dropping quarters until it is done. Write that number down, adjust your machine number and do it again, and again. Often the difference between a major profit margin over a full bag of candy is seriously just 1 number setting on your machine.

I realized that I had to do it no other way. I also realized that at a 5 setting as compared to a 6 setting, was a cost per vend of between .624 and .895 which does not seem like much. However count that across a full bag, then 1 bag per head, and then 40 machines. It becomes serious money. Especially in these times.