GMM wrote:
I need to fit a length of coving along a wall that already has the
same coving on each end wall. Normally, I would mitre but that's not
possible with the others in situ. Nonetheless, it should work fine if
I cut it to the right length and scribe the right profile at each
end.

So what's the problem? Well, when scribing skirting for example, it's
(relatively) easy to transfer the profile as the face of a board is
close to flat, but the curve of the coving makes this damned near
impossible.

Does anyone have a clever trick for this, or is it just a case of
guess it and use plenty of filler when it goes belly up?

Cut a 45 degree mitre as you normally would, and at the root of the mitre
you will see the exact shape that you need to cut. Using something like a
coping saw, follow that profile - and the coving will fit over the other
one. Measure the distance from root to root of the existing coving, mark
the mitre exactly as you would normally (from the root to the end) and do
the same there.

Cash