Well charging what i do works for me,it's easy and ive done it before to under quote atleast if it's say £1 a window your not doing yourself.But i will say the more you quote for, the easier it becomes, as you can compare with others you do.
sorry mate wasnt having a go at you
you are right past experience helps a lot and is important
but you still need something to work from for the future
as long as you put your prices up with inflation £1 a window
will keep you where you are for years
its a very simple plan and you cant expect to much from that