There are great many tutorials on youtube showing how to model various objects - spoon, computer mouse, chair, aerpolane, car body surface, exhaust manifolds etc. But most of these tutorials do now show on how points of 2d/3d geometry were calculated, the tutors just input predetermined numbers so trying to follow these tutorials becomes a very unsatisfying exercise. 

Is there a tutorial that show how to accurately copy an existing shape, going in depth on how to actually determine points of geometry, guide curves, etc?