Mr Marlin only builds 8 to 10 trumpets a year , all are adjustable these days . He has told me numerous times that a box call is a challenge to get what you want out of a piece of wood and that Trumpets are a mechanical deal , make the dimensions the same and you always turn out a good trumpet , so in his description they are not about skill , just repeating measurements with tight tolerances. I am sure this is after you decide which measurements work best for you and this is where the learning curve is !
Then we have to learn a musical instrument to get the sounds we want out of one .