It's just an easy way for me to calculate an estimate..
15-25 is for labor , insurance, and so on..not equpt. over head I don't really have a lot been luck and able to buy at the end of the year to save on the taxes.
Yes it costs more to install more sprays in the same area as it would to just install rotors. That is why I go by my 35/65 formula.
Yes if I have to bore or the layout of the site is a mess, large trees and rocks.. I charge more and have an added cost for the bore and increase my cost by 25% for the trees and rocks..
Percentages is what I go by, because I can try to stay with in my margin alll the time..
I have tried to go by how much per piece of material ( Elbows, wire, Funny pipe) and have included the cost average in my formulas.but I believe that the time I spent in my formulas will save me time and $$$ in the long run. At least I hope so..It's all a #'s game