Ah, well, you see, if I draw it by hand then I end up with even more unpleasantly flat and/or bumpy bits than if I use Béziers :-) A lot of the aim of all the above was to compensate for my lack of pre-existing skill in the normal ways of doing the job.

Now that doesn't make any sense to me, as you can clearly see when there's a bump in the curves, as you are using that vision to correct the computer graphics.

So what I'd do is sketch lightly in pencil the shape, it'd be a bit wrong, so I'd correct and correct and correct with the pencil finally firming up the Right shape with a heavier pencil stroke. Much quicker than trying to do the same on the computer, but still doesn't require perfected mind to hand skills...

If you can see where the bump is on the computer and correct you can do that on paper, it make take many iterations to find the 'right one' but iterations are much quicker with a few pencil strokes on paper than point click stretch move/insert data for each iteration of finding the curve on the computer....

A pencil sketch on a grid can help computer transfer too (though more relevant for improving 'by eye' than the scan onto a different layer and trace option, I routinely sketch over grids on paper to improve putting curves directly on my curve unfriendly cad program)...

I guess the problem with scan and trace, rather than computer by eye or sketch then transfer to computer by eye is there are extra stages in scanning and tracing and fixing the trace.. whereas going straight for by eye with computer curves does it in one - but only if you're good enough!